Remove keystone_plugin.py

As far as I can tell this file is not referenced anywhere, so
in the interest of keeping clean repositories, I am removing it.
Update keystone server recipe to use networks lib

Finding the IP address of a named interface is a relatively useful
and generic function. Therefore have moved this code to
openstack-common library.
Update the repo to use openstack-identity naming

As the name of this repo has changed from keystone to
openstack-identity update the README, resources, and providers to
reflect this change.
Add a default backend for trust

This change simply makes trust backend configuration configurable.
Update db recipe to use openstack-ops-database

With the addition of the openstack-ops-database cookbook, installation
of mysql::client and mysql::ruby should be handled there.
Update keystone.conf to reflect Grizzly changes

This change moves keystone.conf forward to Grizzly. In addition, as
the comments provided in the openstack/keystone.git source are quite
helpful, this change seeks to make this template as consitent as
possible with the sample source provided upstream.

With the development of support for conf.d directories in Oslo, this
file will hopefully be broken out accordingly.