Nix::CopyClosure: Fix sshOpts for oldCopyTo().

This is necessary in order to support deployments for systems using
pre-1.8 versions of Nix, so we should propagate those options there as
well.

I've duplicated the splitting of the NIX_SSHOPTS environment variable
instead of adding an import referencing SSH::sshOpts because the
function is going to be removed eventually and that way we don't miss
anything.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>