Openstackclient usage and caching

Currently the openstack_clients module caches authorization for all OS clients. There's a decorator in that file that can be used to catch 'unauthorized' errors and retry the current operation after clearing that cache. Need to determine if this is an approach everyone's ok with (it was the first thing came to mind when i was doing the summit demo) and then use it where appropriate (probably in the `serialize` functions that use the clients.