pipeline: Fix --cpu-threads option
pipeline: Fix --cpu-threads option

The --cpu-threads setting was not taking effect as the scheduler was not made
current for the calling thread.

Ensure the TBB scheduler object is on the stack when running TBB code.

broadinstitute/firepony,NVlabs/firepony,NVlabs/firepony,NVlabs/firepony,broadinstitute/firepony,broadinstitute/firepony,broadinstitute/firepony,NVlabs/firepony