Only load necessary instance info for use in sync power state

During sync power state, instance is refreshed from the db. If the
instance gets deleted, this can result in InstanceInfoCacheNotFound
being thrown due to info_cache being loaded and therefore refreshed.

Sync power state does not make use of any extra instance attrs, so
this problem can be avoided by not loading any extra attrs in the
first place.

Two callers of _sync_instance_power_state() are updated to not load
extra attrs. 1) The periodic sync and 2) the lifecycle event handler.

Change-Id: I150bd95da65263981608dd9a033232bd142e737f
Closes-Bug: #1367845