Sort `machine ls` output by machine name

At the moment in the `machine ls` output, the order of appearance of the machines is not predictable due to go routine implementation.

This pull request fix this, sorting machine by names (case insensitive).
A better name for this might be `HostListItem` or something like that. "State" is an overloaded term – I was confused about what this had to do with the host state (running, stopped, etc).

I would also argue that this struct should live in commands.go too – it is part of the functionality of the `machine ls` command.