Commander: raise CommandError instead of log in a couple places.
Commander: raise CommandError instead of log in a couple places.

- The end result is mostly same for the user, but is more correct.
- One visible change is that an unrecognised commands passed on the
  command line to Commander will now cause an early exit and non-zero
  exit code, like any other command error.
- This change also corrects a duplicate error log message for exceptions
  raised from python expressions.

flit/pyOCD,pyocd/pyOCD,flit/pyOCD,pyocd/pyOCD