slurm: impose timelimit on cleanup jobs (15min)
slurm: impose timelimit on cleanup jobs (15min)

Cleanup should never take longer than 15 minutes. This helps SLURM's
scheduler when there are reservations in place.


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PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild