Don't log traceback on rpc timeout.

Don't log a traceback in the rpc layer after a timeout() occurs while
waiting on a response to a call().  Let the caller get the exception and
decide whether it should be logged or not.

Fix bug 1158920.

Change-Id: I0387ab48899627cbc3eb1d7187067472ddefc1bf
Sync rpc from oslo-incubator.

Updates include:

* Enabling the rpc message envelope.
* Improved logging for timeouts
* fixes in the zmq driver

Change-Id: I0b2ab1acff1fea9c07a33da176cf6a11ed8a3f2c
Sync everything from oslo-incubator.

Change-Id: If602b424086abb3edbd4703bc0e3befedbf37925
Merge "Don't log traceback on rpc timeout."
Merge "Sync rpc from oslo-incubator."
Merge "Sync everything from oslo-incubator."