Machine: Add mount command for Windows

The FUSE+SSHFS approach used in #4018 to mount remote volumes on Linux clients should be supported on Windows as well.

To help get this started, I forked a GUI app that used an analogous Dokany+SSH.NET approach, and added a CLI. Using this, it is possible to mount all volumes on the remote docker machine as drives.

Here's some Powershell I ran to test:

$ip = docker-machine ip
$l = [int][char]"M"
docker volume ls --format "{{.Mountpoint}}" | % {
    $arglist = "-d $([char]$l) -r $_ -h $ip -u root -x"
    echo $arglist
    start-process -NoNewWindow -FilePath "./sshfs.exe" -RedirectStandardInput ./pass.txt -ArgumentList $arglist
    $l = $l + 1
}

Which mounts all volumes from the docker-machine instance locally

Note that I'm ssh-ing in with a password for the root user, which I manually created. The docker user has no access to the volume folders, and Dokan does not have an analog for the allow_root option from SSHFS as far as I'm aware. Probably in order to do this properly you need a dedicated user that has access to the volume folders, or you should just give docker access.

Overall the approach is probably not as nice as #4018, given the relative immaturity of FUSE on Windows and the hacked together sshfs CLI, but it would be useful for Windows users looking to work with volumes on a remote docker machine.