Work in progress: new version of the ipcluster plugin to drop the SGE requirement

The NFS partition is used instead to be able to run:

    ipcluster engines -n numproc

on each non-master node of the cluster.

TODO:

- update the documentation
- find out why running the notebook locally using the fetched json definition does not work (security group configuration issue?)
- review the configuration: would it be better to leave the default configuration instead?

This is an early pull request to collect feedback from others, especially @minrk before moving further with the documentation update.

Also a question to Min: would it be possible to restart all the engines of the cluster from the controller? Would this require to configure the ssh mode [1] instead? If so, where is the API to shutdown and restart all the active engines?

[1] http://ipython.org/ipython-doc/dev/parallel/parallel_process.html#using-ipcluster-in-ssh-mode