This makes adding roaming tests easier if they don't strictly conform
to the existing test structure. By adding connect/roam helpers future
tests will have a bit more control on whats being tested.
Before setting the address, wait for the interface to go down. This
fixes somewhat rare cases where setting the address returns -EBUSY
and ultimately breaks the neighbor reports.
All tests which could avoid calling scan() directly have been
changed to use the 'full_scan' argument to get_ordered_network.
This was done because of unreliable scanning behavior on slower
systems, like VMs. If we get unlucky with the scheduler some beacons
are not received in time and in turn scan results are missing.
Using full_scan=True works around this issue by repeatedly scanning
until the SSID is found.
