Add centos7 molecule instance for train/c7/py2 use-case

We had to make some changes like [1][2] to use get-hash with c7
for train. While we are still running those train/c7 jobs this
should help let us know if we break something for py2 support.

[1] https://review.opendev.org/c/openstack/tripleo-repos/+/808217
[2] https://review.opendev.org/c/openstack/tripleo-repos/+/809159

Change-Id: I7a0ef0fdbac3ad654dc29753929d78cf01e9b05a

molecule/default/converge.yml

@@ -12,6 +12,7 @@
         # TODO: fix yum_config to correctly report changed state and uncomment
         # the line below which disables molecule idemptotence test.
         - molecule-idempotence-notest
+      when: ansible_distribution_major_version is version(8, '>=')
 
     - name: "Check get_hash"
       tripleo.repos.get_hash:

molecule/default/molecule.yml

@@ -6,6 +6,8 @@ driver:
 platforms:
   - name: instance
     image: quay.io/centos/centos:stream8
+  - name: instance_c7
+    image: quay.io/centos/centos:centos7
 provisioner:
   name: ansible
 verifier: