##### 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
""" Determines if the cache files have expired, or if it is still valid """
        if os.path.isfile(self.cache_path_cache):
            mod_time = os.path.getmtime(self.cache_path_cache)
            current_time = time()
            if (mod_time + self.cache_max_age) > current_time:
                if os.path.isfile(self.cache_path_inventory):
                    return True
        return False
    def read_settings(self):
        """ Reads the settings from the cobbler.ini file """
        if(self.ignore_settings):
            return
        config = ConfigParser.SafeConfigParser()
        config.read(os.path.dirname(os.path.realpath(__file__)) + '/cobbler.ini')
        self.cobbler_host = config.get('cobbler', 'host')
        self.cobbler_username = None
        self.cobbler_password = None
        if config.has_option('cobbler', 'username'):
            self.cobbler_username = config.get('cobbler', 'username')
        if config.has_option('cobbler', 'password'):
            self.cobbler_password = config.get('cobbler', 'password')
        
        cache_path = config.get('cobbler', 'cache_path')
        self.cache_path_cache = cache_path + "/ansible-cobbler.cache"
        self.cache_path_inventory = cache_path + "/ansible-cobbler.index"
        self.cache_max_age = config.getint('cobbler', 'cache_max_age')
    def parse_env_vars(self):