Moar docs, exception catching, change deps, fix key-name

Two more deps needed, and catch a pickle exception so we can throw the following error... TODO: implement better error handling !

I've also modified the default key-name because it's more likely to be the same as the openstack username and not the linux username... Added a bit of help for that as well as debug when the key doesnt exist...

Thanks for the last updates ! It works like a charm now...
Let's raise an exception instead of trying to interpolate weird bash scripts.