Use normal socket file permissions instead of polkit

Use normal socket file permissions instead of polkit

The default (on RHEL/CentOS) is to use polkit but this is only useful
for GUI support or for fine grained API access control.  As we don't
require either we can achieve identical control using plain old unix
filesystem permissions.

I've merged Sven's changes from https://review.openstack.org/484979
and https://review.openstack.org/487150.

As we need to be careful with the libvirtd option quoting I think it's
best to do this in puppet-tripleo instead of t-h-t yaml.

The option to override the settings from t-h-t remains.

Co-Authored-By: Sven Anderson <sven@redhat.com>
Reverts I91be1f1eacf8eed9017bbfef393ee2d66771e8d6

Closes-bug: 1696504

Change-Id: I507bdd8e3a461091562177403a2a55fcaf6694d2
Depends-On: I17f6c9b5a6e2120a53bae296042ece492210597a