Tests: fix test_forward_zones in test_xmlrpc/test_dns_plugin
    
    Class test_forward_zones in ipatests/test_xmlrpc/test_dns_plugin
    was using DNS zone 'fwzone2.test.' and expected to get warning
    'Forwarding policy conflicts with some automatic empty zones.'
    (aka 'DNSForwardPolicyConflictWithEmptyZone').
    
    This does not make sense because 'test.' zone is not listed in IANA registry
    'Locally-Served DNS Zones':
    http://www.iana.org/assignments/locally-served-dns-zones/locally-served-dns-zones.xhtml
    
    To fix this I simply removed the warning from set of expected results.
    
    Original ticket:
    https://fedorahosted.org/freeipa/ticket/6213
    
    Backported to ipa-4-3:
    https://fedorahosted.org/freeipa/ticket/6317
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>