Users may have an external swift proxy already available (i.e. radosgw
from already existing ceph, or hardware appliance implementing swift
proxy). With this change user may specify an environment file that
registers the specified urls as endpoint for the object-store service.
The internal swift proxy is left as unconfigured.
Change-Id: I5e6f0a50f26d4296565f0433f720bfb40c5d2109
Depends-On: Ia568c3a5723d8bd8c2c37dbba094fc8a83b9d67e