Improve help strings for sslutils module

As https://review.openstack.org/#/c/71997/ got merged, we need
to update oslo-incubator to make projects using oslo.messaging
and sslutils working.

Change-Id: I9f49dc08df01a27c54f1ebe2a7c7cb8c4b889018
Merge "Improve help strings for sslutils module"