Avoid vm instance shutdown when power state is NOSTATE

* nova/compute/manager.py (_sync_power_states): Log the condition
where we can retrieve the state from the hyperviser, rather than
stopping the VM.

Related grizzly commits are 95e77703 and ad101ce5

Fixes bug: 1085771
Change-Id: I5fb9fdc6bcde729c00c4931960ed0de3b8fa189d
Merge "Avoid vm instance shutdown when power state is NOSTATE" into stable/folsom