Add nmtui & nmcli prompt to 'myip' output when no IP address found #96

[phillxnet]

Usability enhancement to prompt folks to use NetworkManager command line tools when our 'myip' helper finds no IP address.

Fixes #96
Ready for review.

Testing

Edited a local installer instance of myip as per proposed change and tested as per issue text:

[phillxnet]

Linking to a related, in part, documentation issue regarding static ip setup:
rockstor/rockstor-doc#358

[FroggyFlox]

@phillxnet ,
Thanks for taking care of that one!
I only have minor style suggestion in case it reads better to you.

[phillxnet]

Final testing

An installer was build with this patch pre-applied. The VM enacted an ethernet cable unplugged scenario (see link-status below), to effect no dhcp available via no ethernet connection. An install was then carried out, effectively with-out the ethernet cable plugged in.

The 'myip' utility reacted as intended:

nmtui was then used to

1. Configure a static ip
2. enable this connection.
   The VM was then instructed to re-connect, live, the ethernet cable via:

And the consequent "nmcli" output indicated a transition to a wired carrier:

nmcli device show | grep WIRED.PROPERTIES.CARRIER
WIRED-PROPERTIES.CARRIER:               on

Thus the resulting static IP was applied to the newly live (freshly plugged in) connection and the Rockstor Web-UI was accessible via the static IP set via nmtui; including after a reboot.

Caveat

Post our static ip test above we have a not directly related failure in console messaging on future boot messages:

This can and should be addressed in it's own issue and relates to rockstor-core code that re-writes our console message.

[EDIT]. Note that this message missing the static ip set was only observed after the first reboot. Subsequent reboots had the expected entry for the non localloop address:

[phillxnet]

@FroggyFlox Given the above functional end-to-end test I think we are good on this one. Thanks again for the review and I'll merge directly.