add concurrent_bazel.sh runner

tools/docker_runners/examples/concurrent_bazel.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+# Copyright 2021 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+
+# This wrapper allows running concurrent instances of bazel build/test by running
+# bazel under a docker container.
+# This is especially useful for running bazel RBE builds, since inside
+# the container, bazel won't have access to local build cache.
+
+# Usage:
+# tools/docker_runners/examples/concurrent_bazel.sh ANY_NORMAL_BAZEL_FLAGS_HERE
+
+set -ex
+
+# change to grpc repo root
+cd "$(dirname "$0")/../../.."
+
+# use the default docker image used for bazel builds
+export DOCKERFILE_DIR=tools/dockerfile/test/bazel
+
+# Bazel RBE uses application default credentials from localhost to authenticate with RBE servers. Use a trick to make the credentails accessible from inside the docker container."
+APPLICATION_DEFAULT_CREDENTIALS_DIR="$HOME/.config/gcloud"
+export DOCKER_EXTRA_ARGS="-v=${APPLICATION_DEFAULT_CREDENTIALS_DIR}:/application_default_credentials:ro -e=GOOGLE_APPLICATION_CREDENTIALS=/application_default_credentials/application_default_credentials.json"
+
+# Run bazel inside a docker container (local git workspace will be mounted to the container)
+tools/docker_runners/run_in_docker.sh bazel "$@"