ipatests: test_epn: Fix package installation
    
    EPN functionality is provided as separate package
    freeipa-client-epn, but it is not installed during setup. This resolves
    this behaviour.
    
    Signed-off-by: Michal Polovka <mpolovka@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>