Ad-hoc offloading to a server

[Christine Lemmer-Webber <cwebber@dustycloud.org>]

Sometimes I've wanted to offload builds ad-hoc to another server, like
so:

  guix build mypackage --offload-to=cwebber@beefybuilder.org

This would offload by ssh'ing into that server and doing the offloading
there, but it's a more explicit user specified location.

Thoughts?  Would this be a worthwhile feature?

 - Christine

PS: I suppose despite being a more explicit operation, I suppose the
/etc/guix/acl file can't be avoided under our current security model,
because we're still trusting that the remote location is trustworthy
enough to put this build result in our store as the result associated
with this input.  One user could, otherwise, screw over all others.