Don't attempt to install ruby-switch in ubuntu 14.04 onwards

ruby-switch is gone from 14.04 onwards. I don't know too much about chef so if you need me to add any tests / change anything just point me in the right direction.
This is unnecessary, on the basis that among all of the cookbooks in use on a project, there will be many conditional resources, and if all the ones that *weren't* in use logged like this, it would be chaos.