Allow forceDelete to delete running instances

Currently attempting to force delete a running instance
fails while a normal delete can succeed. This changes the
behaviour of force_delete so any instance can be deleted
and not just ones which have already been soft deleted.

Also catch InstanceIsLocked exceptions at the API layer
and now also don't need to catch InstanceInvalidState
exceptions since they are no longer raised

DocImpact: forceDelete will now delete any instance and not
  just ones which have already been soft deleted

Change-Id: I06a476701ccb47d8f7fd6e43c394ccb3fac2b3aa
Closes-Bug: 1351001
Merge "Allow forceDelete to delete running instances"