Allow ranges of CPUs in cpus_allowed option

Allow ranges of CPUs in cpus_allowed option

For a larger number of CPUs, it's a bit of a bother having to set
each one individually. Plus, you typically want to bind to a range of
CPUs, to keep the job core local (or whatever your preference). So extend
cpus_allowed to take ranges of CPU numbers as well. Now you can do:

cpus_allowed=0-7

and have your job confined to CPUs 0 through 7.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>