Fix confirm_resize() mock in compute tests

Looks like this intended to mock out confirm_resize() but forgot a
crucial bit. If we time out call()s in the fake RPC driver when there
are no consumers for a topic, the test_delete_in_resized() test fails
because of this.

blueprint: oslo-messaging
Change-Id: Iedc540170f6df29050764f497afa1ba07fed997a
Merge "Fix confirm_resize() mock in compute tests"