fix VM power state to be NOSTATE when instance not found

* nova/compute/manager.py (_sync_power_states): Revert what looks
like an inadvertent change that was part of commit 95e77703.
Also log the condition.

Fixes bug: 1085771
Change-Id: Ic6eeb9207323f05b93f0b613bd1bddd681ad8ce5
Merge "fix VM power state to be NOSTATE when instance not found"