Add fast8 tox env

This was taken from the nova project, fast8 will allow running flake8
tests on a subset of changes (only HEAD) which is quicker.

Change-Id: I9069edad75befcd4995a1c23924e2856da56c216
Signed-off-by: Arnaud M <arnaud.morin@gmail.com>

tools/flake8wrap.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+#
+# A simple wrapper around flake8 which makes it possible
+# to ask it to only verify files changed in the current
+# git HEAD patch.
+#
+# Intended to be invoked via tox:
+#
+#   tox -epep8 -- -HEAD
+#   or
+#   tox -efast8
+#
+
+if test "x$1" = "x-HEAD" ; then
+    shift
+    files=$(git diff --name-only HEAD~1 | tr '\n' ' ')
+    echo "Running flake8 on ${files}"
+    echo ""
+    diff -u --from-file /dev/null ${files} | flake8 "$@"
+else
+    echo "Running flake8 on all files"
+    echo ""
+    exec flake8 "$@"
+fi

tox.ini

@@ -33,6 +33,12 @@ commands =
   doc8 doc/source
   flake8 {posargs} . {toxinidir}/tools/sync_db.py
 
+[testenv:fast8]
+description =
+  Run style checks on the changes made since HEAD~. For a full run including docs, use 'pep8'
+commands =
+  bash tools/flake8wrap.sh -HEAD
+
 # Deprecated
 [testenv:unit-postgresql]
 description =