[dhcp_relay] Fix dhcp_relay restart error while add/del vlan

[yaqiangz]

Why I did

In device that doesn't have dhcp_relay service, restart dhcp_relay after add/del vlan would encounter failed

How I did it

Add support to check whether device is support dhcp_relay service.

How to verify it

1. Unit test

tests/vlan_test.py::TestVlan::test_show_vlan PASSED                      [ 71%]
tests/vlan_test.py::TestVlan::test_show_vlan_brief PASSED                [ 71%]
tests/vlan_test.py::TestVlan::test_show_vlan_brief_verbose PASSED        [ 71%]
tests/vlan_test.py::TestVlan::test_show_vlan_brief_in_alias_mode PASSED  [ 71%]
tests/vlan_test.py::TestVlan::test_show_vlan_brief_explicit_proxy_arp_disable PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_show_vlan_config PASSED               [ 72%]
tests/vlan_test.py::TestVlan::test_show_vlan_config_in_alias_mode PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_vlan_with_invalid_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_vlan_with_exist_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_del_vlan_with_invalid_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_del_vlan_with_nonexist_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_member_with_invalid_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_member_with_nonexist_vlanid PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_exist_port_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_nonexist_port_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_nonexist_portchannel_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_portchannel_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_add_rif_portchannel_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_with_vxlanmap_del_vlan PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_del_vlan PASSED           [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_del_nonexist_vlan_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_add_del_vlan_and_vlan_member PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_add_del_vlan_and_vlan_member_in_alias_mode PASSED [ 72%]
tests/vlan_test.py::TestVlan::test_config_vlan_proxy_arp_with_nonexist_vlan_intf_table PASSED [ 72%]

2. Build and install in device
   2.1 On device dhcp_relay is running

admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo config vlan add 1001
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo config vlan del 1001
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo config vlan add 1001
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hset "DHCP_RELAY|Vlan1001" "dhcpv6_servers@" "fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4"
1
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{'dhcpv6_servers@': 'fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4'}
admin@bjw-can-720dt-2:~$ sudo config vlan del 1001
Restarting DHCP relay service...
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo config vlan add 1001
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hset "DHCP_RELAY|Vlan1001" "dhcpv6_servers@" "fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4"
1
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{'dhcpv6_servers@': 'fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4'}
admin@bjw-can-720dt-2:~$ sudo config vlan del 1001 --no_restart_dhcp_relay
Usage: config vlan del [OPTIONS] <vid>
Try "config vlan del -h" for help.

Error: Can't delete Vlan1001 because related DHCPv6 Relay config is exist
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hdel "DHCP_RELAY|Vlan1001" "dhcpv6_servers@"
1
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-720dt-2:~$ sudo config vlan del 1001 --no_restart_dhcp_relay
admin@bjw-can-720dt-2:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}

2.2 On device dhcp_relay is not running

admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo config vlan add 1001
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo config vlan del 1001
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo config vlan add 1001
admin@bjw-can-7050qx-1:~$ show vlan bri
+-----------+--------------+---------+----------------+-------------+-----------------------+
|   VLAN ID | IP Address   | Ports   | Port Tagging   | Proxy ARP   | DHCP Helper Address   |
+===========+==============+=========+================+=============+=======================+
|      1001 |              |         |                | disabled    |                       |
+-----------+--------------+---------+----------------+-------------+-----------------------+
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hset "DHCP_RELAY|Vlan1001" "dhcpv6_servers@" "fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4"
1
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{'dhcpv6_servers@': 'fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4'}
admin@bjw-can-7050qx-1:~$ sudo config vlan del 1001
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo config vlan add 1001
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hset "DHCP_RELAY|Vlan1001" "dhcpv6_servers@"^C
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hset "DHCP_RELAY|Vlan1001" "dhcpv6_servers@" "fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4"
1
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{'dhcpv6_servers@': 'fc02:2000::1,fc02:2000::2,fc02:2000::3,fc02:2000::4'}
admin@bjw-can-7050qx-1:~$ sudo config vlan del 1001 --no_restart_dhcp_relay
Usage: config vlan del [OPTIONS] <vid>
Try "config vlan del -h" for help.

Error: Can't delete Vlan1001 because related DHCPv6 Relay config is exist
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hdel "DHCP_RELAY|Vlan1001" "dhcpv6_servers@"
1
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ sudo config vlan del 1001 --no_restart_dhcp_relay
admin@bjw-can-7050qx-1:~$ sudo sonic-db-cli CONFIG_DB hgetall "DHCP_RELAY|Vlan1001"
{}
admin@bjw-can-7050qx-1:~$ show vlan bri
+-----------+--------------+---------+----------------+-------------+-----------------------+
| VLAN ID   | IP Address   | Ports   | Port Tagging   | Proxy ARP   | DHCP Helper Address   |
+===========+==============+=========+================+=============+=======================+
+-----------+--------------+---------+----------------+-------------+-----------------------+

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[yaqiangz]

@jcaiMR Could you please help to review this PR?