Fix typos and make script more extensible

- Don't hardcode /dev/da1; allow user to provide a mix of devices and
  paths via $*
- Allow bs= to be random
- Provide random size= value if user specified a path (this was required
  for later versions of fio)
- Remove randwrite,rw (not supported on later versions of fio)
- Check for fio and print out a message if it can't be found
- cat out the jobfile before calling fio for debugging purposes.
- Allow ioengine to be a random ioengine that is supported by
  FreeBSD

Sponsored by: EMC / Isilon Storage Division
Add tmpdir cleanup to trap

Sponsored by: EMC / Isilon Storage Division