Use dynamic includes for speedup
Use dynamic includes for speedup

Now that Ansible 2.x allows for dynamic includes, we can drive a hard
split between the RHEL 6 and RHEL 7 STIG work. This speeds up gate jobs
and avoids situations where a variable is defined in one STIG playbook
versus another.

Implements: blueprint security-rhel7-stig
Change-Id: If3cf9f2154055a316c0764556d57a0dde9e061f4

major/openstack-ansible-security,major/openstack-ansible-security