support for git+ssh protocol when the ssh key is encrypted

[wadsaek]

when using, for example, nh os switch git+ssh://git@github.com/..., nh shows openssh's prompt to enter the passphrase, but then continues with the stopwatch without letting the user to type the mentioned phrase

steps to reproduce: try rebuilding the configuration from a repo using ssh, when your ssh key is encrypted

[wadsaek]

sorry my bad maybe i was entering the wrong passphrase....