Stub out setup_networks_on_host() in compute tests

If we time out call()s in the fake RPC driver when there are no
consumers for a topic, lots of tests fail when we attempt to call()
out to the network service to do setup_networks_on_host().

blueprint: oslo-messaging
Change-Id: I62f855f111c5f69a676e8e3747a9894847d5d27d
Merge "Stub out setup_networks_on_host() in compute tests"