rabbit: add some tests when rpc_backend is set

This change improves test coverage of the rabbit driver for new
value allowed in rpc_backend config option.

Change-Id: I52a8a8beb5b0d32647f52bb21abd5f7164dac2df
Updated from global requirements

Change-Id: I55eed75a9d6a8375823480220b8312eb255e417a
Merge "rabbit: add some tests when rpc_backend is set"
Merge "Updated from global requirements"