Remove EPEL and use RDO instead

This patch removes the epel-release package whenever the pip_install
role is applied and should eliminate package conflicts between RDO
and EPEL. The RDO package path is also adjusted to download the RDO
package from repos.fedorapeople.org (which slashes 3 HTTP redirects
out of the 5 when using rdoproject.org).

This is a breaking change for OSA deployments which are already
deployed on CentOS. Some containers may need to be rebuilt after
making this change.

Related-bug: 1670012
Change-Id: I2e69fac6368c032e237ca35839dd09dab9b0c5c0

releasenotes/notes/replace-epel-df390980c03bbaa8.yaml

@@ -0,0 +1,9 @@
+---
+upgrade:
+  - |
+    The EPEL repository is now removed in favor of the RDO repository.
+
+    **This is a breaking change for existing CentOS deployments.** The ``yum``
+    package manager will have errors when it finds that certain packages that
+    it installed from EPEL are no longer available.  Deployers may need to
+    rebuild container or reinstall packages to complete this change.

vars/redhat-7.yml

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-pip_install_external_repo_key_package: "https://rdoproject.org/repos/openstack-ocata/rdo-release-ocata.rpm"
+pip_install_external_repo_key_package: "https://repos.fedorapeople.org/repos/openstack/openstack-ocata/rdo-release-ocata.rpm"
 
 pip_install_distro_build_packages:
   - gcc
@@ -31,3 +31,4 @@ pip_required_pip_packages:
 pip_install_remove_distro_packages:
   - centos-openstack-release-*
   - centos-release-qemu-ev
+  - epel-release