This patch enables the RHEL 7 STIG content tasks as the default.
Documentation has also been updated to reflect the change and provide
more concise information about what is available with each release.
The OpenStack-Ansible repo is still set to use the RHEL 6 STIG until
some issues with individual roles are resolved.
Implements: blueprint security-rhel7-stig
Change-Id: Ic72d97b87c0fb16646e5a31030404e1a9ad6a469