Enable minimum CentOS repositories
Enable minimum CentOS repositories

The CentOS CI images have many yum repositories enabled by default.
This can cause package conflicts in gate jobs and it doesn't match
what a basic CentOS system would look like for an OpenStack-Ansible
deployer.

This patch disables all repositories for the ansible-role-jobs and
only enables base, epel, and updates. This allows individual roles
to add extra repositories when they need them.

Related-Bug: 1708493
Change-Id: I2ac5a9c463991e4668a3e7608831c1944377e85e

openstack-infra/project-config,openstack-infra/project-config