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/tests/unit/test_utils.py

@@ -55,7 +55,7 @@ class TestUtils(testtools.TestCase):
             file_obj.close()
 
     def test_prettytable(self):
-        class Struct:
+        class Struct(object):
             def __init__(self, **entries):
                 self.__dict__.update(entries)