ipa host-add --ip-address: properly handle NoNameservers
    
    When ipa host-add --ip-address is called but no DNS server is able to answer
    for the reverse zone, get_reverse_zone raises a NoNameservers exception.
    The exception is not managed by add_records_for_host_validation, and this
    leads to the command exiting on failure with an InternalError:
        $ ipa host-add testhost.ipadomain.com --ip-address 172.16.30.22
        ipa: ERROR: an internal error has occurred
    A traceback is also logged in httpd error_log.
    
    This commit properly handles the exception, and adds a test.
    
    https://pagure.io/freeipa/issue/7397
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>