[MRG]: 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:

- <del>update the documentation</del>
- <del>find out why running the notebook locally using the fetched json definition does not work (security group configuration issue?)</del> configured the SG to open the controller ports
- review the configuration: would it be better to leave the default configuration instead?
- <del>change the packer config to selection between json (default), pickle or msgpack + documentation.</del>

This is an early pull request to collect feedback from others, especially @minrk before moving further with the documentation update.

Also some questions for Min:

- <del>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?</del> Basic restart plugin implemented, better version will require some refactoring upstream in IPython
- <del>is there a cleaner way to shutdown some engines (with a timeout before calling the `pkill` command) in the `on_remove_node` method?</del> Good enough for now.

[1] http://ipython.org/ipython-doc/dev/parallel/parallel_process.html#using-ipcluster-in-ssh-mode