Updated openstack/openstack
Project: openstack/oslo.messaging  68f8857f30c0f9840d8b68df25a03c9e3fb2d938

RPC server doc: use the blocking executor

The eventlet executor need additional code to make the RPC server sample
work. Using the blocking executor makes things easier to setup for a
newcomer.

Change-Id: I56dfa54a178962d4ced34e2f15eaf9312b7087cc