Don't use git diff --quiet to detect local change

It seems that there is a bug in (old?) versions of git, particularily in
the one that is shipped with Ubuntu Precise (1.7.9.5) that (sometimes?)
makes the exit code of git diff incorrect.

Change-Id: Id2286147529f1072fe4ceff3fc5200aeb30267a1
Related-Bug: #1264422
Related-Bug: #1410434

tools/integration.sh

@@ -89,7 +89,7 @@ for PROJECT in $PROJECTS ; do
     sudo chown -R $USER $REPODIR/$SHORT_PROJECT
     (cd $REPODIR/requirements && python update.py $REPODIR/$SHORT_PROJECT)
     pushd $REPODIR/$SHORT_PROJECT
-    if ! git diff --quiet ; then
+    if ! git diff --exit-code > /dev/null; then
         git commit -a -m'Update requirements'
     fi
     popd