Fix yum_repository for more centos6 EOL fallout

Change:
- Use a version specific vars file to specify archive url for EPEL.

Test Plan:
- ci_complete

Signed-off-by: Rick Elrod <rick@elrod.me>

test/integration/targets/yum_repository/vars/CentOS-6.yml

@@ -0,0 +1,10 @@
+yum_repository_test_package: sl
+yum_repository_test_repo:
+  name: epel
+  description: EPEL yum repo
+  baseurl: https://archives.fedoraproject.org/pub/archive/epel/{{ ansible_facts.distribution_major_version }}/$basearch
+
+yum_repository_epel:
+  description: Extra Packages for Enterprise Linux {{ ansible_facts.distribution_major_version }} - $basearch
+  mirrorlist: https://mirrors.fedoraproject.org/metalink?repo=epel-{{ ansible_facts.distribution_major_version }}&arch=$basearch
+  gpgkey: file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-{{ ansible_facts.distribution_major_version }}