Properly detect and report failures while trying to start slothd, and remove the lock file before trying to start it if it isn't running.
Properly detect and report failures while trying to start slothd, and remove the lock file before trying to start it if it isn't running.

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