Change Cray mpi_fini failure logic

Treat Cray MPI job calling exit() without mpi_fini() as fatal error for
that specific task and let srun handle all timeout logic.
Previous logic would cancel the entire job step and srun options
for wait time and kill on exit were ignored. The new logic provides
users with the following type of response:

$ srun -n3 -K0 -N3 --wait=60 ./tmp
Task:0 Cycle:1
Task:2 Cycle:1
Task:1 Cycle:1
Task:0 Cycle:2
Task:2 Cycle:2
slurmstepd: step 14927.0 task 1 exited without calling mpi_fini()
srun: error: tux2: task 1: Killed
Task:0 Cycle:3
Task:2 Cycle:3
Task:0 Cycle:4
...

bug 1171