Add a sanity test for shellcheck

Start by checking the scripts in tools/run_tests/helper_scripts.

templates/tools/dockerfile/test/sanity/Dockerfile.template

@@ -29,7 +29,8 @@
         libtool ${"\\"}
         curl ${"\\"}
         python-virtualenv ${"\\"}
-        python-lxml
+        python-lxml ${"\\"}
+        shellcheck
   RUN pip install simplejson mako
   
   #======================================

tools/dockerfile/test/sanity/Dockerfile

@@ -81,7 +81,8 @@ RUN apt-get update && apt-get install -y \
       libtool \
       curl \
       python-virtualenv \
-      python-lxml
+      python-lxml \
+      shellcheck
 RUN pip install simplejson mako
 
 #======================================

tools/run_tests/sanity/check_shellcheck.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Copyright 2017 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.
+
+
+set -e
+
+ROOT="$(dirname "$0")/../../.."
+
+DIRS=(
+    'tools/run_tests/helper_scripts'
+)
+
+for dir in "${DIRS[@]}"; do
+  find "$ROOT/$dir/" -name "*.sh" -type f -print0 | xargs -n1 -0 shellcheck
+done

tools/run_tests/sanity/sanity_tests.yaml

@@ -3,6 +3,7 @@
 - script: tools/run_tests/sanity/check_cache_mk.sh
 - script: tools/run_tests/sanity/check_owners.sh
 - script: tools/run_tests/sanity/check_sources_and_headers.py
+- script: tools/run_tests/sanity/check_shellcheck.sh
 - script: tools/run_tests/sanity/check_submodules.sh
 - script: tools/run_tests/sanity/check_test_filtering.py
 - script: tools/run_tests/sanity/check_tracer_sanity.py