Fix new issues with unit tests

- Create custom test suite based on platform
- Use the custom suite for all tests
- Update tox.ini to install pywin32

tox.ini

@@ -5,13 +5,19 @@ skip_missing_interpreters = True
 [testenv]
 platform = linux
 commands =
-    python setup.py test
+    python setup.py test --test-suite tests.TestSuite
 
 [testenv:py3-win]
 platform = win
 commands =
-    python setup.py test --test-suite tests.test_plat_win
+    python pip install pywin32
+    python setup.py test --test-suite tests.TestSuite
 
 [testenv:py27]
 deps =
     configparser
+
+[flake8]
+exclude = .tox,env,build
+max-line-length = 120
+ignore = E731,E203,E501,W503