##### SUMMARY

SyntaxWarning over using is for comparison of literals. The fix is simple and is a good beginner issue.

```
contrib/inventory/cobbler.py:218: SyntaxWarning: "is not" with a literal. Did you mean "!="?
  if this_dns_name is not None and this_dns_name is not "":
```

##### ISSUE TYPE

- Bug Report

##### COMPONENT NAME

cobbler

##### ANSIBLE VERSION

devel branch
cobbler --dns-name is set for each cobbler system.   If a system
appears with two DNS names we do not add it twice because we don't want
ansible talking to it twice.  The first one found will be used. If no
--dns-name is set the system will NOT be visible to ansible.  We do
not add cobbler system names because there is no requirement in cobbler
that those correspond to addresses.
Tested with Cobbler 2.0.11.
Changelog:
    - 2015-06-21 dmccue: Modified to support run-once _meta retrieval, results in
         higher performance at ansible startup.  Groups are determined by owner rather than
         default mgmt_classes.  DNS name determined from hostname. cobbler values are written
         to a 'cobbler' fact namespace
    - 2013-09-01 pgehres: Refactored implementation to make use of caching and to
        limit the number of connections to external cobbler server for performance.
        Added use of cobbler.ini file to configure settings. Tested with Cobbler 2.4.0
"""
#
#
#
#
import argparse
import os
import re
from time import time
import xmlrpclib
import json
from ansible.module_utils.six import iteritems
from ansible.module_utils.six.moves import configparser as ConfigParser
orderby_keyname = 'owners'  
class CobblerInventory(object):