Add "scpfrom src dst" action to freebsd-vm-boot task

[ihoro]

No description provided.

[markjdb]

Thanks for the PR! A few comments, since I thought about this a bit already but haven't done anything about it.

• The notion of an "action" is kind of a hack, I would be happy to see some alternative interface.
• It would be nice to have both scp-to and scp-from.
• I would really really like to see 9pfs support land in FreeBSD soon, which would make scp less necessary. There is a lot of functionality that will be unlocked by that feature.
• Is it possible to collect all arguments after the action, instead of just two?

I will spend some time on this soon, I just haven't had much time these past few days to work on bricoler.