setting up.  First chunk: we don't want to skip straight to reboot if the
node is plab.  Second chunk: we need to run both plabnode alloc and remote
vnodesetup on plab nodes.  Third chunk: we have to ssh to the vnode, not
the pnode, on plab nodes, to make sure we make it to the correct sliver.
Not sure how this last affects jails, so I special-cased it for plab.