Add cpus_allowed option

cpumask can be cumbersome to use, since it requires you to calculate
a decimal mask to pass to fio. So add a cpus_allowed option that
takes a text list of allowed cpus, ala: cpus_allowed=1,3,8 will set
the affinity mask for CPUS 1, 3, and 8.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/README b/README
index a56f633..a646de0 100644
--- a/README
+++ b/README
@@ -129,6 +129,7 @@
 	ratemin=x	Quit if rate of x KiB/sec can't be met
 	ratecycle=x	ratemin averaged over x msecs
 	cpumask=x	Only allow job to run on CPUs defined by mask.
+	cpus_allowed=x	Like 'cpumask', but allow text setting of CPU affinity.
 	fsync=x		If writing with buffered IO, fsync after every
 			'x' blocks have been written.
 	end_fsync=x	If 'x', run fsync() after end-of-job.