Add support for specifying -currentHost or -host <hostname>

I have absolutely no idea if this is a good idea or not (or if this
change even works), but I was trying to add some osx_default rules
that needed defined with the -currentHost param as well as without.

An example of a rules would be L#99 here:
https://github.com/mathiasbynens/dotfiles/blob/master/.osx#L99-L100