Misc tb-set-tarfiles client side fixes.
Misc tb-set-tarfiles client side fixes.

This includes create a large local filesystem (using mkextrafs) if the
target directory starts with "/local".

These changes where suppose to go in with my initial commit, but I
forgot to push from my test node to my devel tree before rebasing and
hanse they didn't make it in.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome