Fix LDAP authentication

ldap class, that is responsable for authentication was not called correctly.
Now parameters from config file are used properly to find ldap authentication
 class correctly.
Add corresponding test.

kqueen/auth/common.py

@@ -19,7 +19,7 @@ def get_auth_instance(name):
     auth_config = config.get("AUTH", {}).get(name, {})
 
     # If user auth is not specified clearly, use local
-    if name == 'local' or None:
+    if name == 'local' or name is None:
         auth_config = {'engine': 'LocalAuth', 'param': {}}
 
     module = importlib.import_module('kqueen.auth')