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: I5f60f9cf321fcccdb9801f4678fd3cb922812548
Depends-On: I5e6f0a50f26d4296565f0433f720bfb40c5d2109