test/integration/client: test exec calls metric

Signed-off-by: Andrew Keesler <akeesler@vmware.com>

test/integration/client/testdata/exec-plugin-not-executable.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+# Copyright 2018 The Kubernetes 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 file is not executable, and therefore it will not be run.
+exit 1

test/integration/client/testdata/exec-plugin.sh

@@ -23,4 +23,6 @@ if [[ -n "${EXEC_PLUGIN_OUTPUT_FILE-""}" ]]; then
   exit
 fi
 
-echo "$EXEC_PLUGIN_OUTPUT"
+echo "${EXEC_PLUGIN_OUTPUT-""}"
+
+exit "${EXEC_PLUGIN_EXEC_CODE-0}"