Allow keystone to run from apache

Provide a template for running keystone as a mod_wsgi process and enable
it from configuration.

Based on: https://review.openstack.org/#/c/36474/
Also-by: zhang-hare <zhuadl@cn.ibm.com>
Implements: blueprint devstack-setup-apache-keystone

Change-Id: Icc9d7ddfa4a488c08816ff4ae0b53c0134a1016b
Merge "Allow keystone to run from apache"