Reminder that release notes are built from commits

This patch introduces a new tools/releasenotes_tox.sh script for the
tox -e releasenotes test environment. It will detect when there are
uncommitted release notes and print a reminder to commit them.

Change-Id: I54af12d7eb20b37263e23443900745884cffacea

tools/releasenotes_tox.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+rm -rf releasenotes/build
+
+sphinx-build -a -E -W \
+    -d releasenotes/build/doctrees \
+    -b html \
+    releasenotes/source releasenotes/build/html
+
+UNCOMMITTED_NOTES=$(git status --porcelain | \
+    awk '$1 == "M" && $2 ~ /releasenotes\/notes/ {print $2}')
+
+if [ "${UNCOMMITTED_NOTES}" ]
+then
+    cat <<EOF
+
+REMINDER: The following changes to release notes have not been committed:
+
+${UNCOMMITTED_NOTES}
+
+While that may be intentional, keep in mind that release notes are built from
+committed changes, not the working directory.
+
+EOF
+fi
+
+exit ${BUILD_RESULT}