Use flake8 for testing

Start using flake8 for style guide enforcement.

Change-Id: I9d7c89498c10e682acf0f75bad20dfd4bb6152b5

test-requirements.txt

@@ -9,3 +9,4 @@ stestr>=1.0.0 # Apache-2.0
 testscenarios>=0.4
 testtools>=2.2.0
 oslotest>=3.2.0 # Apache-2.0
+flake8-import-order>=0.13 # LGPLv3

tox.ini

@@ -22,6 +22,7 @@ sitepackages = True
 
 [testenv:pep8]
 whitelist_externals = bash
+commands = flake8
 
 [testenv:cover]
 setenv =
@@ -40,11 +41,19 @@ commands = python setup.py build_sphinx
 commands = {posargs}
 
 [flake8]
-exclude = .venv,.tox,dist,doc,*.egg,build
+exclude = .venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 show-source = true
-
-[pep8]
-ignore = E731,E226,E123
+# E129 visually indented line with same indent as next logical line
+# E731 do not assign a lambda expression, use a def
+# W504 line break after binary operator
+ignore = E129,E731,W504
+# H106: Don't put vim configuration in source files
+# H203: Use assertIs(Not)None to check for None
+# H204: Use assert(Not)Equal to check for equality
+# H205: Use assert(Greater|Less)(Equal) for comparison
+# H904: Delay string interpolations at logging calls
+enable-extensions=H106,H203,H204,H205,H904
+import-order-style = pep8
 
 [testenv:lower-constraints]
 deps =