Negative Taskmanager Resize/Migration fixes.

* Revert barrier should be right after Verify_RESIZE is confirmed, but
  before confirming flavor for a resize action.
* Verify nova server status before restarting mysql.
  If anything goes wrong during resize/migrate actions, taskmanager
  first checks that the Nova server status is ACTIVE and only then make
  the call to restart MySQL.

Fixes: bug #1102523

Change-Id: Ibca436d7fdcdef9f1afcec111da84891cd15353c