This is a follow-on to I3279c3b5cb8cf26d390835fd0a7049bc43ec40b5
As discussed in the referenced issue, the blank return and
AttributeError here is the correct way to determine a recently deleted
image. We don't need to catch the ClientError as that won't be raised
any more. Getting a value for the state would indicate it wasn't
deleted.
This bumps the moto base requirement to ensure we have this behaviour.
Change-Id: I2d5b0ccb9802aa0d4c81555a17f40fe8b8595ebd