CI: check for possible diff after make vendor

We can commit broken vendoring here because there is no actual test to
verify that the vendor directory is clean after make vendor.

PR[1] had a renovate bug[2] which causes it to not run go mod tidy, this was
not caused by CI because of it.

[1] https://github.com/containers/common/pull/1555
[2] https://github.com/containers/automation/pull/148

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

common/.cirrus.yml

@@ -52,6 +52,7 @@ testing_task:
     - export PATH="$PATH:$GOPATH/bin"
     - gpg --batch --passphrase '' --quick-gen-key tester@localhost default default never
     - make vendor
+    - hack/tree_status.sh
     - make build
     - make build-cross
     - make test

common/hack/tree_status.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -e
+
+SUGGESTION="${SUGGESTION:-run \"make vendor\" and commit all changes.}"
+
+STATUS=$(git status --porcelain)
+if [[ -z $STATUS ]]
+then
+	echo "tree is clean"
+else
+	echo "tree is dirty, please $SUGGESTION"
+	echo ""
+	echo "$STATUS"
+	echo ""
+	echo "---------------------- Diff below ----------------------"
+	echo ""
+	git --no-pager diff
+	exit 1
+fi