Add fast8 ability to tox

This patch adds the same tox -efast8 check for testing pep8 violations
against future patches.  This is a bit faster, because it only tests what
has changed in your current repo.

Change-Id: I6eff6b5f57d947f8c1d0c832227d0f7e15d4bc6f

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

@@ -26,6 +26,10 @@ commands = flake8 {posargs}
 install_command = {[testenv:common-constraints]install_command}
 commands = flake8 {posargs}
 
+[testenv:fast8]
+envdir = {toxworkdir}/pep8
+commands = {toxinidir}/tools/fast8.sh
+
 [testenv:venv]
 commands = {posargs}
 
@@ -64,8 +68,7 @@ commands = oslo_debug_helper {posargs}
 
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
-
 show-source = True
 ignore = E123,E125
 builtins = _
-exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build
+exclude=.venv,.git,.tox,dist,doc/*,*openstack/common*,*lib/python*,*egg,build