
Be default sshtb now tries to ssh to the specified node via protocol version 2.
It will try protocol version 1 if a v2 connection/auth fails.  This was a
little messy to implement since sshtb now has to fork the first ssh attempt and
wait to see if it succeeds (all the fun of dealing with signals and killing
off the child ssh process and whatnot).

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