use rpm -i instead of yum install for epel7

On BaseOS CI systems, `yum install` for the epel7 rpm does not work.
Instead, use `rpm -i` which should work on any system.  We should not
need to use `yum install` here because the epel7 setup rpm does not have
additional dependencies.
In addition, the rpm download sometimes returns 403 - I think it is because
multiple tests run in parallel in BaseOS CI, resulting in too many
download attempts in too short a period of time - so introduce a retry
to mitigate the situation.

Signed-off-by: Rich Megginson <rmeggins@redhat.com>

tests/tasks/enable_epel.yml

@@ -3,10 +3,18 @@
 - block:
     - name: Create EPEL {{ ansible_distribution_major_version }}
       # yamllint disable-line rule:line-length
-      command: yum install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest-{{ ansible_distribution_major_version }}.noarch.rpm
+      command: rpm -iv https://dl.fedoraproject.org/pub/epel/epel-release-latest-{{ ansible_distribution_major_version }}.noarch.rpm
       args:
         warn: false
         creates: /etc/yum.repos.d/epel.repo
+      register: __epel_status
+      # sometimes the rpm download returns a 403 - I think it is when too
+      # many parallel jobs attempt the download from the same controller in
+      # too short a period of time, so the epel server throttles additional
+      # downloads - use a retry here to mitigate
+      until: __epel_status is success
+      retries: 6
+      delay: 10
 
     - name: Enable EPEL 7
       command: yum-config-manager --enable epel