Avoid false positives with test_server_connectivity_live_migration

The test has been modified to check VM status and connectivity before
obtaining the measured network downtime.
With this change, the network downtime is measured after network
connectivity is recovered after the live-migration is completed,
avoiding false positive results.

Change-Id: I855534b2662d015715d9acd1e4b98614589df6db
1 file changed