IPA-EPN: Add mail-test option for testing sending live email
    
    To make testing easier for administrators the --mail-test option
    can be used to send live e-mail from ipa-epn. It sends mail
    to the smtp_admin user processing the template with dummy data.
    
    https://pagure.io/freeipa/issue/3687
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Francois Cami <fcami@redhat.com>