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/exceptions.py

@@ -42,8 +42,7 @@ from glanceclient.openstack.common._i18n import _
 
 
 class ClientException(Exception):
-    """The base exception class for all exceptions this library raises.
-    """
+    """The base exception class for all exceptions this library raises."""
     pass
 
 
@@ -118,8 +117,7 @@ class AmbiguousEndpoints(EndpointException):
 
 
 class HttpError(ClientException):
-    """The base exception class for all HTTP exceptions.
-    """
+    """The base exception class for all HTTP exceptions."""
     http_status = 0
     message = _("HTTP Error")