Add WSGISocketPrefix to apache keystone config

I think since probably fdf1cffbd5d2a7b47d5bdadbc0755fcb2ff6d52f
devstack on RHEL6 fails and it comes down to:

---
2014-07-17 05:05:49.235 | +++ openstack role create admin -f value -c id
2014-07-17 05:05:49.615 | ERROR: cliff.app Service Unavailable (HTTP 503)

[Thu Jul 17 15:05:46 2014] [error] [client 10.0.2.15]
  (13)Permission denied: mod_wsgi (pid=30125): Unable to connect to WSGI
   daemon process 'keystone-public' on
   '/etc/httpd/logs/wsgi.30098.0.1.sock' after multiple attempts.
---

The apache user doesn't have permissons to this directory.  Adding
WSGISocketPath to /var/run solves it

Change-Id: If4b74019b6bd389b576fc981154bb1b3aa471c9b
Merge "Add WSGISocketPrefix to apache keystone config"