[CC] Send rollback request to source node when migration preparation fails on destination.

Fixes EUCA-5889.
[CC] Finish implementation of sending rollback request to source node when migration preparation fails on destination.

Fixes EUCA-5889.
[NC] Handle rollback requests on source node.

Fixes EUCA-5889.
Merge remote-tracking branch 'origin/testing' into dev/juphoff/evac-test
Merge remote-tracking branch 'origin/testing' into dev/juphoff/evac-test