This adds support for configuring horizon for WebSSO when keystone
federation with OpenID Connect is enabled. This patch just exposes
some new parameters to use puppet-horizon for configuration. The
sample environment file for OpenID Connect federation is also updated
to use the new parameters. Some of the sample defaults were updated
to more closely match the URLs that horizon expects.
Change-Id: I7c3ee6b54cc0c9653742c3ce1de60b2851d1fe68