BZ#841555 A migration failure with an "AttributeError" exception.

Libvirt sometimes send the SUSPENDED/SUSPENDED_PAUSED event
after RESUMED/RESUMED_MIGRATED (when VM status is PAUSED
when migration completes, see qemuMigrationFinish function).
In this case self._dom is None because the function
_waitForIncomingMigrationFinish didn't update it yet.

Change-Id: I3b7ed13c6dc8d1d590449118cf167290f4630070
Signed-off-by: Gal Hammer <ghammer@redhat.com>
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/6901
Reviewed-by: Peter V. Saveliev <peet@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Tested-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>