Enable H407,H305,H307,E122 ignore E123

After bumping the hacking version to the 0.9.x series ignores were
added for several rules. This commit fixes the violations for a subset
of these rules and re-enables the checks.

E123 is ignored because this rule is ignored in the default pep8 by
default, due to a lack of consensus around it.

Change-Id: I8f14cd2ca6afc38d3fe8ee758272071111022896
diff --git a/tools/colorizer.py b/tools/colorizer.py
index a3a0616..e7152f2 100755
--- a/tools/colorizer.py
+++ b/tools/colorizer.py
@@ -42,10 +42,10 @@
 """Display a subunit stream through a colorized unittest test runner."""
 
 import heapq
-import subunit
 import sys
 import unittest
 
+import subunit
 import testtools