Remove hardcoded paths

* added helper functions to return variables for system we are running on
* removed hardcoded paths and socket type

This will allow us to expand to other operating systems without changing too many files. 
This is really an implementation detail of jujuc, and would probably be better off defined there. There are quite a few places that create sockets, and this should not be used for all of them.

I'm surprised that this would work on Windows, BTW, as the socketPath arg to jujuc.NewServer is a file path, which will not be valid as the address argument to a tcp connection. I suspect that it might be better to do some more abstraction closer to jujuc.