Updated openstack/openstack
Project: openstack/oslo.messaging  c0fde4749964b1d071c687887f172d5321dc3470

remove default=None for config options

In the cfg module default=None is set as the default value.

Change-Id: I5de0c1ddeeaccde8183ec130c85524f5b57f6f74
Closes-Bug: #1323975