SLOW=${SLOW:-no}
FAIL_ON_ERROR=${FAIL_ON_ERROR:-true}
-MPIRUN=$(which mpirun 2>/dev/null) || true
+MPIRUN=${MPIRUN:-$(which mpirun 2>/dev/null || true)}
MPI_USER=${MPI_USER:-mpiuser}
SHARED_DIR_LOGS=${SHARED_DIR_LOGS:-""}
MACHINEFILE_OPTION=${MACHINEFILE_OPTION:-"-machinefile"}