sshutils: fix AttributeErrors in SSHGlob class

self.paramiko -> self.ssh
ipcluster: pep8 clean-up
ipcluster: raise exception if IPython isnt installed
ipcluster: newline cleanup
ipcluster: move inner function to class
Merge branch 'ipy-plugin-refactoring' into develop

closes gh-204
ipcluster: add null versions of unimplemented methods

The IPython plugins subclass the default plugin in order to take
advantage of the threadpool setup. In this case it's important to
override all ClusterSetup callbacks implemented by the default plugin in
order to avoid executing the same callbacks multiple times.

Updated the IPython plugins with null versions of all callbacks
implemented by the default plugin.
plugins: raise NotImplementedError in unimplemented methods
New plugin to install python packages with pip
Add missing override for the on_remove_node method
Documentation for the pypackage plugin