Sort `machine ls` output by machine name

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Rename HostState struct to HostListItem

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Move HostListItem from host.go to command.go

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Merge pull request #87 from ggiamarchi/machine-ls-sort

Sort `machine ls` output by machine name