Check cherry-pick hashes in pep8 tox target

This adds a tools/ script that checks any cherry-picked hashes
on the current commit (or a provided commit) to make sure that
all the hashes exist on at least master or stable/.* branches.
This should help avoid accidentally merging stable backports
where one of the hashes along the line has changed due to conflicts.

Change-Id: I4afaa0808b75cc31a8dd14663912c162281a1a42

tools/check-cherry-picks.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+#
+# A tool to check the cherry-pick hashes from the current git commit message
+# to verify that they're all on either master or stable/ branches
+#
+
+hashes=$(git show --format='%b' --quiet $1 | sed -nr 's/^.cherry picked from commit (.*).$/\1/p')
+checked=0
+branches+=""
+for hash in $hashes; do
+    branch=$(git branch -a --contains "$hash" 2>/dev/null| grep -oE '(master|stable/[a-z]+)')
+    if [ $? -ne 0 ]; then
+        echo "Cherry pick hash $hash not on any master or stable branches"
+        exit 1
+    fi
+    branches+=" $branch"
+    checked=$(($checked + 1))
+done
+
+if [ $checked -eq 0 ]; then
+    if ! grep -q '^defaultbranch=stable/' .gitreview; then
+        echo "Checked $checked cherry-pick hashes: OK"
+        exit 0
+    else
+        if ! git show --format='%B' --quiet | grep -qi 'stable.*only'; then
+            echo 'Stable branch requires either cherry-pick -x headers or [stable-only] tag!'
+            exit 1
+        fi
+    fi
+else
+    echo Checked $checked cherry-pick hashes on branches: $(echo $branches | tr ' ' '\n' | sort | uniq)
+fi

tox.ini

@@ -56,6 +56,7 @@ commands =
   bash -c "! find doc/ -type f -name *.json | xargs grep -U -n $'\r'"
   # Check that all included JSON files are valid JSON
   bash -c '! find doc/ -type f -name *.json | xargs -t -n1 python -m json.tool 2>&1 > /dev/null | grep -B1 -v ^python'
+  bash tools/check-cherry-picks.sh
 
 [testenv:fast8]
 description =