SONiC Zero ports PR tracker

[liorghub]

Allow system without ports in config db run without errors.
Related PRs:

PR title	State	Status	Dependencies	Unitest	Owner
[snmp] Allow system with no ports in config db run without errors		tests are failing due to depedency	sonic-net/sonic-py-swsssdk#109	done, part of the PR	@liorghub
[port_util] Allow system without ports in config db run without errors		checkers passed	None	done, part of the PR	@liorghub
[sonic-cfggen] Allow cfggen to work on system without ports		checkers passed	None	done, part of the PR	@liorghub
[show] Allow system with no ports in config db run without errors		checkers passed	None	no need, minor change	@liorghub
[portsyncd] when no ports on config db on init - continue and set PortConfigDone		vs tests are failing	None	no need, minor change	@tomer-israel
[swss]: Allow portsyncd to run on system without ports		merged	None	None	@liorghub
[port_util] Fix issue in function get_interface_oid_map		merged	None	no need, minor change	@liorghub