Using AMQP-based RPC can be an overkill in case of ironic, especially
when used standalone. This change allows using a built-in JSON RPC
implementation instead.
This implementation does not currently support the object indirection
API, which does not seem to be used anywhere anyway.
The standalone and API test jobs are changed to use JSON RPC.
Story: #2004874
Task: #29141
Change-Id: I7cc95935d6bdae43fab5dfbd544c8e6d65fcc38d