##### 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
def __init__(self):
        """ Main execution path """
        self.conn = None
        self.inventory = dict()  
        self.cache = dict()  
        self.ignore_settings = False  
        
        self.parse_env_vars()
        self.read_settings()
        self.parse_cli_args()
        
        if self.args.refresh_cache:
            self.update_cache()
        elif not self.is_cache_valid():
            self.update_cache()
        else:
            self.load_inventory_from_cache()
            self.load_cache_from_cache()
        data_to_print = ""
        
        if self.args.host:
            data_to_print += self.get_host_info()
        else:
            self.inventory['_meta'] = {'hostvars': {}}
            for hostname in self.cache:
                self.inventory['_meta']['hostvars'][hostname] = {'cobbler': self.cache[hostname]}
            data_to_print += self.json_format_dict(self.inventory, True)
        print(data_to_print)
    def _connect(self):