Add system tests for service account credentials (#51)

scripts/decrypt-secrets.sh

diff --git a/scripts/decrypt-secrets.sh b/scripts/decrypt-secrets.sh
new file mode 100755
index 0000000..e02bfc1
--- /dev/null
+++ b/scripts/decrypt-secrets.sh
@@ -0,0 +1,27 @@
+#!/bin/bash
+
+# Copyright 2015 Google Inc. All rights reserved.
+#
+# 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.
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+ROOT=$( dirname "$DIR" )
+
+# Work from the project root.
+cd $ROOT
+
+openssl aes-256-cbc -k "$1" \
+    -in system_tests/secrets.tar.enc \
+    -out system_tests/secrets.tar -d
+tar xvf system_tests/secrets.tar
+rm system_tests/secrets.tar