Feature/jmg multithread fix

This is the revised commit, removing all the merge weirdness. I've tested it on our OpenStack cluster and it works fine, providing the Vagrantfile template is changed to comment out the hostname (which is an issue separate from this fix).

It can be tested by running and checking that the hostnames of the machines are correct, and that the tasktracker is running on each machine (/etc/init.d/hadoop-0.20-mapreduce-tasktracker status) and that the jobtracker is running on the master machine (/etc/init.d/hadoop-0.20-mapreduce-jobtracker status)