When EPEL install flag is not set

The flag dnf_install_epel was being used to predicate installation
of the EPEL RPM repo package, but not preventing the installation
of configuration for access to EPEL.  This small patch completes
the job.

Updates the overcloud host configure CI job to install EPEL mirrors,
since it was previously relying on this buggy behaviour.

Change-Id: Ib417837d0772338b16ea9f7f2540549f277d5de8

ansible/roles/dnf/tasks/local-mirror.yml

@@ -38,9 +38,11 @@
   loop:
     - epel.repo
     - epel-modular.repo
+  when: dnf_install_epel | bool
 
 - name: Update cache
   dnf:
     name: []
     update_cache: yes
   become: True
+  when: dnf_install_epel | bool

playbooks/kayobe-overcloud-host-configure-base/overrides.yml.j2

@@ -103,8 +103,6 @@ dnf_custom_repos:
     baseurl: http://packages.treasuredata.com/3/redhat/$releasever/$basearch
     gpgkey: https://packages.treasuredata.com/GPG-KEY-td-agent
     gpgcheck: yes
-# Don't install EPEL repositories.
-dnf_install_epel: false
 # Enable DNF Automatic.
 dnf_automatic_enabled: true
 {% endif %}