ipatests: check that ipa-healthcheck warns if no dna range is set
    
    Added testcase to verify that ipa-healthcheck tool displays a
    warning if no DNS range is set. It previously just reported at the
    SUCCESS level that no range was set.
    
    Issue: freeipa/freeipa-healthcheck#60
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Francois Cami <fcami@redhat.com>