Working on Data Flow (step 5)

* Testing subsequent tasks

TODO:
* More tests
* Actions refactoring

Change-Id: Ib057e76479cac065cc430e4b5af60db314c3a3f2
Use oslo.messaging for AMQP communications

Ported task executor to oslo.messaging. The executor module is
replaced with RPC server/client named Executor and ExecutorClient
respectively to handle task execution. The old executor module is
deleted.  The engine is modified to use the ExecutorClient to send
task requests over the transport to the Executor. The launcher is
modified to start the new Executor.

Change-Id: Ibce01813e51c2220c45e05bb820b4729027446a3
Implements: blueprint mistral-oslo-messaging
Merge "Working on Data Flow (step 5)"