Stress test 015 need to check partition size

["Marcelo E. Magallon" <marcelo.magallon@xxxxxxxxxxx>]

Hi,

 015 is trying to create a 50MB data section on the device, but don't
 check if the operation is sucessful:

 mkfs -t xfs -f -d size=50m $SCRATCH_DEV >/dev/null

 016 does check, but exits with an error instead of using _notrun.

-- 
Marcelo