Adds scenario for hotplug nic in network_basic_ops

New scenario test verifying add network to an active VM.

Test is added to network_basic_ops module as most of the code already exists
there.

Partially Implements: blueprint neutron-advanced-scenarios

Change-Id: I5946134de7038a3a7da236dac7018c211cbcce97
Merge "Adds scenario for hotplug nic in network_basic_ops"