tests: handle returning different response for the same request
tests: handle returning different response for the same request

Allow programming different responses for the same request when called
multiple times. This is useful for example for shutdown tests - first
domain is running, but after issuing shutdown request is is not.

marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client