Ensure the instance is unpaused when bless throws an exception.

When bless throws an exception Cobalt should ensure that the
source instance is returned to its previous state (usually running).
Before blessing Cobalt determines the state of the instance, and if
it was not paused Cobalt will call 'unpause' on the instance if bless
raises an exception.

Fixes OS-194

Change-Id: I184edf20d64425fd646ba6af3786ecbced0b5565