Replace manual SSH with SSH2 package

[getdave]

Currently we build up manual SSH commands and execute them via shelljs. Often this involves quite complex templating and can become confusing. It also doesn't provide that much protection in terms of errors and feedback for the user.

Consider removing all manually executed SSH commands in favour of

https://github.com/mscdex/ssh2

Commands can be executed in series directly on the remote machine via a single SSH connection.