Clean up compute API image_create

The _image_create() code in compute manager is the only place where
db.instance_test_and_set is used.. which was added before
'expected_task_state' support was added to instance_update.  By
switching to use self.update(), we can also take advantage of it doing
the state change notification for us.

The instance update and the compute RPC call have been moved out of
_create_image() and into snapshot() and backup() to support a future
cells patch.

Change-Id: Ib6603f732d28e49cb6f351447da5f6e41615dea5
Fix typos in docstring

* code in bin/

* code in nova/api/

Change-Id: Ic643d640b66785d4bb54defcddc3d2312292bfdf
Revert "Use testr setuptools commands."

This reverts commit c945b71929d7dc872ea27103ca8b6ec3d5cc7cd5
which caused the unit test command to always exit sucessfully.

Change-Id: I410cbc878675503f0ce6e50bddc4fd0552370c46
Merge "Revert "Use testr setuptools commands.""
Merge "Fix typos in docstring"
Merge "Clean up compute API image_create"