Added endpoint for binding identity services.

This changes adds an endpoint that is used to specify a bind_interface
or host to bind the indentity services to.

The following change in the identity cookbook is dependent on this one:
https://review.openstack.org/#/c/78019/

blueprint increase-ip-binding-flexibility

Change-Id: I12798ebcee0eb5b226a51d7824fbb172c50fdf37
Merge "Added endpoint for binding identity services."