Make sure periodic task sync_power_states continues on error

If an instance sync_power action fails with an exception, no more
instances will be synced. If the failure is permanent, this will block
other instances from having their power states synced for as long as
this keeps happening.

Make sure to catch and log such exceptions and then continue with the
next instance.

Change-Id: Ie3cf5d7f590cb680e712d76b7a32c630e82f362d
Closes-Bug: #1228160