bug: `vyos_ssh` source doesn't work on VyOS 1.4+

Looks like they got rid of the Python script that we grab leases from and rolled that into a different one. https://github.com/vyos/vyos-1x/commit/1f1915fca2734d47e2df653ef10bc14fbce74173

No more JSON output :cry: so gotta parse `tabulate` output now.