orchard ssh vm: introduce exec mode

[edigaryev]

Example use-case:

% cat test.sh
#!/bin/sh

ls

% orchard ssh vm macos 'sh -s' < test.sh 2>/dev/null 
Desktop
Documents
Downloads
Library
Movies
Music
Pictures
Public
actions-runner

Resolves #60.

[fkorotkov]

Wow. Could you please add examples to docs as well?

Maybe a simple one like orchard ssh vm macos 'uname -a' and the complex one like in your comment.

Also in case of orchard ssh vm macos 'uname -a', will the ssh session exit? Or it will be hanging until we exit 0?

[edigaryev]

Wow. Could you please add examples to docs as well?

Added in 0772750.

Also in case of orchard ssh vm macos 'uname -a', will the ssh session exit? Or it will be hanging until we exit 0?

It will exit since there are no more processes that are running (e.g. command interpreter), yes.