You need fabric (fabfile.org) installed to make this work.

To start/stop the masters, run:
$ fab masters {start|stop}

To start/stop the slaves, run:
$ fab slaves {start|stop}

The masters file and the slaves file now can use any of the following formats:

# Comment
host1
user@host2
user2@host3:port
user3@hosts4 -p port

Also, on all the machines the HADOOP_HOME should be ~/hadoop.