Added new mirror repo rhel-7-server-ansible-2.4-rpms for ansible install

[wabouhamad]

Ansible package will no longer be available in the aos.repo. In OCP 3.9 it will be provided in the ansible repo which is mirrored:
https://mirror.openshift.com/enterprise/rhel/rhel-7-server-ansible-2.4-rpms/

• created new repo file: image_provisioner/playbooks/roles/repo-install/files/rhel7-server-ansible.repo
• updated role create-repo to install this new repo
• updated role ansible-update to install ansible only from the newly created rhel7-server-ansible repo

More details are also summarized here:

• Need to enable ansible repo on control host for 3.9 openshift-docs#7890
• https://bugzilla.redhat.com/show_bug.cgi?id=1547973

[wabouhamad]

@mffiedler PTAL