Update common docstrings to match guidelines

Per http://docs.openstack.org/developer/hacking/
and http://www.python.org/dev/peps/pep-0257/

Without extra blank line in multi-line docstrings
based on http://lists.openstack.org/pipermail/openstack-dev/2014-February/028156.html

Blueprint: reduce-flake8-ignored-rules

Change-Id: Ic970fff3b66c357170f45e817d080fdb37c63d6e
Merge "Update common docstrings to match guidelines"