Set rollback status early in update if triggered

Before when rollback was triggered during stack update, the stack continued to
have status UPDATE_IN_PROGRESS, and only at the very end flipped to
ROLLBACK_COMPLETE.
This patch sets the stack state to ROLLBACK as soon as
rollback is started to notify the user properly on the action being
performed.

Change-Id: Idbd78a3a2a8d0c32fb26c7d0c38c87857d1565d8
Closes-Bug: #1316558
Remove usages of threads in DummyThreadGroup

The patch removes creation of threads in the DummyThreadGroup class
during tests, returning a fake thread object instead. It removes some
race condition triggering tracebacks during tests.

Closes-Bug: #1330292
Change-Id: I3214816a4173670d22385dbe67cc016d74c2ce18
Merge "Remove usages of threads in DummyThreadGroup"
Merge "Set rollback status early in update if triggered"