Fix race when testing for ETXTBSY writing to ${n0} (process image) by making
sure the process has been started beforehand with pgrep

pkill the process afterwards to make sure it's dead when the unlink is run
(not strictly required, but I was being conservative)

MFC after: 1 week
Reviewed by: Darius O'Conner, mjohnston
Sponsored by: EMC / Isilon Storage Division