Allow relative DNS name in NS validator

Precallback validator was failing when a zone-relative name was
used as a NS record (for example record "ns" in a zone "example.com").
However, this is valid in BIND and we should allow it as well.

Imports in dns module had to be switched to absolute imports
(available from Python 2.5) to deal with a conflict of IPA dns
module and dnspython module.

https://fedorahosted.org/freeipa/ticket/2630

ipalib/plugins/dns.py

@@ -18,9 +18,12 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from __future__ import absolute_import
+
 import netaddr
 import time
 import re
+import dns.name
 
 from ipalib.request import context
 from ipalib import api, errors, output
@@ -1488,7 +1491,11 @@ def zone_is_reverse(zone_name):
 
     return False
 
-def check_ns_rec_resolvable(name):
+def check_ns_rec_resolvable(zone, name):
+    if not name.endswith('.'):
+        # this is a DNS name relative to the zone
+        zone = dns.name.from_text(zone)
+        name = unicode(dns.name.from_text(name, origin=zone))
     try:
         return api.Command['dns_resolve'](name)
     except errors.NotFound:
@@ -1707,12 +1714,12 @@ class dnszone_add(LDAPCreate):
             raise errors.ValidationError(name='name-server',
                     error=unicode(_("Nameserver address is not a fully qualified domain name")))
 
-        if not 'ip_address' in options and not options['force']:
-            check_ns_rec_resolvable(nameserver)
-
         if nameserver[-1] != '.':
             nameserver += '.'
 
+        if not 'ip_address' in options and not options['force']:
+            check_ns_rec_resolvable(keys[0], nameserver)
+
         entry_attrs['nsrecord'] = nameserver
         entry_attrs['idnssoamname'] = nameserver
         return dn
@@ -1878,7 +1885,8 @@ class dnsrecord(LDAPObject):
         nsrecords = entry_attrs.get('nsrecord')
         if options.get('force', False) or nsrecords is None:
             return
-        map(check_ns_rec_resolvable, nsrecords)
+        for nsrecord in nsrecords:
+            check_ns_rec_resolvable(keys[0], nsrecord)
 
     def _ptrrecord_pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
         ptrrecords = entry_attrs.get('ptrrecord')