repos: disable EPEL by default

EPEL is not required when deploying OpenStack with RDO repositories.
In fact, it's causing some packaging conflicts for some dependencies,
and having it installed might cause some deployment failures.

To avoid this situation, let's disable its setup by default to improve
our user experience but add a note about why we disable it by default.

Change-Id: I2f06619e74f5e07889e29a82401344dda67ef51a

manifests/repo/redhat/redhat.pp

@@ -17,7 +17,8 @@
 # [*manage_epel*]
 #   (optional) Whether to create a predefined yumrepo resource
 #   for the EPEL repository provided by RedHat
-#   Defaults to true
+#   Note: EPEL is not required when deploying OpenStack with RDO.
+#   Defaults to false
 #
 # [*repo_hash*]
 #   (optional) A hash of yumrepo resources that will be passed to
@@ -61,7 +62,7 @@
 class openstack_extras::repo::redhat::redhat(
   $release           = $::openstack_extras::repo::redhat::params::release,
   $manage_rdo        = true,
-  $manage_epel       = true,
+  $manage_epel       = false,
   $repo_hash         = {},
   $repo_defaults     = {},
   $gpgkey_hash       = {},

releasenotes/notes/disable_epel-a07b06048465e7a1.yaml

@@ -0,0 +1,5 @@
+---
+other:
+  - Disable EPEL repository setup by default. Keep the boolean if users
+    want it, but add a note that EPEL is not required when deploying
+    OpenStack with RDO repositories.