Fail hyperkube.sh if any command fails (#1352)

hyperkube.sh is started as part of the `gulp local-up-cluster` task. The
script can fail for example if the docker daemon is not running. This
failure was not reported to the user in anyway. By adding the -e flag we
make sure that the script returns error code if any of the commands
fail. A useful error message is also shown to the user in the example
error case.

build/hyperkube.sh

-#!/bin/bash
+#!/bin/bash -e
 # Copyright 2015 Google Inc. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");