Pep8 environment to run on delta code only

Currently tox -epep8 will run flake8 on whole code.
To make this fast, flake8 support is added for only
updated(delta) code.

Same can be run by "tox -efast8".

Change-Id: I9c55fed32ae3060c21ec278398e9e07fb4a0fe13
Implements: BP tox-pep8-diff-part-only

tools/fast8.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+cd $(dirname "$0")/..
+CHANGED=$(git diff --name-only HEAD~1 | tr '\n' ' ')
+
+# Skip files that don't exist
+# (have been git rm'd)
+CHECK=""
+for FILE in $CHANGED; do
+    if [ -f "$FILE" ]; then
+        CHECK="$CHECK $FILE"
+    fi
+done
+
+diff -u --from-file /dev/null $CHECK | flake8 --diff

tox.ini

@@ -11,6 +11,12 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = ostestr {posargs}
 whitelist_externals = ostestr
 
+[testenv:fast8]
+# Use same environment directory as pep8 env to save space and install time
+envdir = {toxworkdir}/pep8
+commands =
+  {toxinidir}/tools/fast8.sh
+
 [testenv:pep8]
 commands =
     flake8