Global DNS options

Implement API for DNS global options supported in bind-dyndb-ldap.
Currently, global DNS option overrides any relevant option in
named.conf. Thus they are not filled by default they are left as
a possibility for a user.

Bool encoding had to be fixed so that Bool LDAP attribute can also
be deleted and not just set to True or False.

https://fedorahosted.org/freeipa/ticket/2216

ipaserver/plugins/ldap2.py

@@ -67,10 +67,11 @@ SASL_AUTH = _ldap_sasl.sasl({}, 'GSSAPI')
 # OID 1.3.6.1.4.1.1466.115.121.1.7 (Boolean) syntax encoding
 def _encode_bool(self, value):
     def encode_bool_value(value):
+        if value is None:
+            return None
         if value:
             return u'TRUE'
-        else:
-            return u'FALSE'
+        return u'FALSE'
 
     if type(value) in (tuple, list):
         return tuple(encode_bool_value(v) for v in value)