Adjust authentication.rst doc to reference "identity_uri"
Adjust authentication.rst doc to reference "identity_uri"

The "auth_port", "auth_host", and "auth_protocol" variables were
deprecated in favour of a single "identity_uri" variable.

* Adjust authentication.rst doc to reference "identity_uri"

Change-Id: I48de53f21b8d767b276858ed274066015d765f0e
Closes-Bug: #1361613

rajalokan/glance,wkoathp/glance,jumpstarter-io/glance,takeshineshiro/glance,saeki-masaki/glance,stevelle/glance,paramite/glance,kfwang/Glance-OVA-OVF,dims/glance,vuntz/glance,klmitch/glance,JioCloud/glance,darren-wang/gl,openstack/glance,ozamiatin/glance,scripnichenko/glance,openstack/glance,wkoathp/glance,JioCloud/glance,darren-wang/gl,paramite/glance,takeshineshiro/glance,kfwang/Glance-OVA-OVF,klmitch/glance,jumpstarter-io/glance,vuntz/glance,saeki-masaki/glance,dims/glance,openstack/glance,stevelle/glance,sigmavirus24/glance,scripnichenko/glance,ozamiatin/glance,akash1808/glance,akash1808/glance,rajalokan/glance,sigmavirus24/glance