Updated openstack/openstack
Project: openstack/oslo.messaging  1b4d7ad6f2da7bba2d2d72a67745dbee4f2beb09

Cleaned up references to executor specific RPCServer types

In oslo.messaging design phase, it was planned to introduce executor
specific RPCServer types though they were never implemented. References
to those types sneaked into docstrings from the original design
document. Since we're not going to implement those types now, docstrings
should be updated accordingly.

Change-Id: Ic4017bb8f89d47115bb7dc59483e81d26c76212b