hack/boilerplate.sh: fix error handling and use python3 (#2587)

* hack/boilerplate.sh: fix successful return code when call to python fails

* hack/boilerplate.sh: update to python3

python2 is no longer included in most distros and will be removed from
Github Actions Ubuntu images:
https://github.com/actions/runner-images/issues/7402

hack/boilerplate.sh

@@ -1,5 +1,4 @@
 #!/bin/bash
-
 # Copyright 2018 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,16 +12,20 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+set -e
 
 # Ignore these paths in the following tests.
 ignore="vendor\|out"
 BOILERPLATEDIR=./hack/boilerplate
+files=$(python3 ${BOILERPLATEDIR}/boilerplate.py --rootdir . --boilerplate-dir ${BOILERPLATEDIR})
+
 # Grep returns a non-zero exit code if we don't match anything, which is good in this case.
 set +e
-files=$(python ${BOILERPLATEDIR}/boilerplate.py --rootdir . --boilerplate-dir ${BOILERPLATEDIR} | grep -v $ignore)
+relevant_files=$(echo "$files" | grep -v $ignore)
 set -e
-if [[ ! -z ${files} ]]; then
+
+if [[ ! -z ${relevant_files} ]]; then
 	echo "Boilerplate missing in:"
-    echo "${files}"
+    echo "${relevant_files}"
 	exit 1
 fi

hack/boilerplate/boilerplate.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Copyright 2018 Google LLC
 #

hack/boilerplate/boilerplate.py.txt

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Copyright YEAR Google LLC
 #