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

tests/test_xmlrpc/xmlrpc_test.py

@@ -222,7 +222,7 @@ class Declarative(XMLRPC_test):
             )
         try:
             api.Command[cmd](*args, **options)
-        except errors.NotFound:
+        except (errors.NotFound, errors.EmptyModlist):
             pass
 
     def test_generator(self):