Enable flake8 checks

This commit enables new flake8 checks:
* E265  block comment should start with '# '
* H405  multi line docstring summary not separated with an empty line
* E123  closing bracket does not match indentation of opening bracket's line
* H238  old style class declaration, use new style (inherit from `object`)
* E128  continuation line under-indented for visual indent
and makes related changes in the code.

Change-Id: Ie993afc930f6b74d7a990bcaa9fc0e9f5ba1585c

glanceclient/openstack/common/apiclient/client.py

@@ -368,7 +368,7 @@ class BaseClient(object):
 
     @staticmethod
     def get_class(api_name, version, version_map):
-        """Returns the client class for the requested API version
+        """Returns the client class for the requested API version.
 
         :param api_name: the name of the API, e.g. 'compute', 'image', etc
         :param version: the requested API version