Copy in keystone paste if platform_family is RHEL

The openstack-keystone package on RHEL does not include
/etc/keystone/keystone-paste.ini, so if we do not manage this file then
just copy it into /etc/keystone from
/usr/share/keystone/keystone-dist-paste.ini.

Change-Id: Ie85701cdae8b7fa93b8fe7d06423c491aafafd88
Closes-Bug: #1327130