Split keystone mod wsgi config from start/stop

We currently cleanup keystone apache config during stop_keystone
when mod wsgi is enabled, but only create it during initial keystone
configuration.  Grenade expects to be able to stop and start the
service without reconfiguring it, using only the respective functions.
This moves cleanup of config from stop_keystone to cleanup_keystone,
and enables/disables the apache vhost during start/stop.

Closes-bug: #1365105

Change-Id: I9e57c9a763fbdb8c5737decfe797ba0e9894150b
Merge "Split keystone mod wsgi config from start/stop"