Allow underscore in record targets

Makes record target validation less strict and allows underscore.
This is requirement for IPA sites.

https://fedorahosted.org/freeipa/ticket/3550

ipalib/plugins/dns.py

@@ -373,7 +373,7 @@ def _bind_hostname_validator(ugettext, value):
     try:
         # Allow domain name which is not fully qualified. These are supported
         # in bind and then translated as <non-fqdn-name>.<domain>.
-        validate_hostname(value, check_fqdn=False)
+        validate_hostname(value, check_fqdn=False, allow_underscore=True)
     except ValueError, e:
         return _('invalid domain-name: %s') \
             % unicode(e)

tests/test_xmlrpc/test_dns_plugin.py

@@ -677,7 +677,7 @@ class test_dns(Declarative):
                                                                  'srv_part_port' : 123,
                                                                  'srv_part_target' : u'foo bar'}),
             expected=errors.ValidationError(name='srv_target',
-                error=u'invalid domain-name: only letters, numbers, and - ' +
+                error=u'invalid domain-name: only letters, numbers, _, and - ' +
                     u'are allowed. DNS label may not start or end with -'),
         ),
 
@@ -780,7 +780,7 @@ class test_dns(Declarative):
             desc='Try to add invalid CNAME record %r using dnsrecord_add' % (dnsrescname),
             command=('dnsrecord_add', [dnszone1, dnsrescname], {'cnamerecord': u'-.example.com'}),
             expected=errors.ValidationError(name='hostname',
-                error=u'invalid domain-name: only letters, numbers, and - ' +
+                error=u'invalid domain-name: only letters, numbers, _, and - ' +
                     u'are allowed. DNS label may not start or end with -'),
         ),
 
@@ -849,7 +849,7 @@ class test_dns(Declarative):
             desc='Try to add invalid DNAME record %r using dnsrecord_add' % (dnsresdname),
             command=('dnsrecord_add', [dnszone1, dnsresdname], {'dnamerecord': u'-.example.com.'}),
             expected=errors.ValidationError(name='target',
-                error=u'invalid domain-name: only letters, numbers, and - ' +
+                error=u'invalid domain-name: only letters, numbers, _, and - ' +
                     u'are allowed. DNS label may not start or end with -'),
         ),