Switching to using pbs_is_loaded instead of pbs module.
Switching to using pbs_is_loaded instead of pbs module.

This is because:
module load pbs raven-devel-gcc
will override mpiexec if raven-devel-gcc is already loaded,
but pbs_is_loaded will not.

idaholab/raven,idaholab/raven,idaholab/raven,joshua-cogliati-inl/raven,joshua-cogliati-inl/raven,idaholab/raven,joshua-cogliati-inl/raven,idaholab/raven,idaholab/raven,joshua-cogliati-inl/raven,joshua-cogliati-inl/raven,idaholab/raven,joshua-cogliati-inl/raven,joshua-cogliati-inl/raven