Cache swift responses in process_environments_and_files
Cache swift responses in process_environments_and_files

process_environments_and_files retrieves all the environment files from
swift, but those can be referenced from multiple places, and thus be
retrieved multiple time. Cache them direclty here for now, until we fix
the heatclient utility function.

Change-Id: Ibc34bf0afcbf73e3a9c130dbb06c80141048494b

openstack/tripleo-common,openstack/tripleo-common