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

tasks/main.yml

@@ -43,12 +43,4 @@
     tags:
       - always
 
-  - include: rhel6stig/main.yml
-    when:
-      - stig_version == 'rhel6'
-
-  # NOTE(mhayden): RHEL 7 STIG content is still under development. Do not run
-  # these tasks against a production environment at this time.
-  - include: rhel7stig/main.yml
-    when:
-      - stig_version == 'rhel7'
+  - include: "{{ stig_version }}stig/main.yml"