Sync to newer openstack.common.cfg
Sync to newer openstack.common.cfg

Changes since last sync are:

 * New ConfigOpts.find_file() for locating conf files
 * Support for directory source of config files
 * Provide file extension when when looking for files
 * Some refactoring of the cfg cache
 * Add caching to openstack.common.cfg

Change-Id: I5fd483b8d1a6e83f7237507132009d31dd8bcb77

n0ano/gantt,n0ano/gantt