Disable oslo.messaging debug logs

oslo.messaging debug logs are too verbose, turn them off. A similar patch
dropped nova-conductor logs in the gate down from 7MB to under 300K.

Cherry-Pick from oslo-incubator since we are in feature freeze:
Ia12c003dae196e2220a5f6ea768758a75f2ede23 and
Icc61964c6a2b002ac1c8566f174e6a5230674c75

Closes-Bug: #1309626
(cherry picked from commit a24192d90938ea89b8f20132de60e6ad3a4ad447)
Change-Id: I9e6456f1c979d9a57fc7fa93fb290c6a26017373
Merge "Disable oslo.messaging debug logs" into stable/icehouse