Stub out get_console_topic() in test_create_console

Without this, if we time out call()s in the fake RPC driver when there
are no consumers for a topic, then the test just fails.

blueprint: oslo-messaging
Change-Id: Ic085909711b19a05dedb0d7bafbd019bb0448212
Merge "Stub out get_console_topic() in test_create_console"