Sync with latest version of openstack.common.cfg
Sync with latest version of openstack.common.cfg

Changes since last sync:

 - Alphabetize imports in openstack/common/cfg.py
 - make reset() clear defaults and overrides
 - automatically create option groups
 - allow options to be marked as required
 - use a list comprehension instead of map()

Change-Id: I74fac3f66b37ee07bab53bd655c0297f25849979

n0ano/ganttclient