[PATCH] usbtest: report errors in iso tests

This patch (as693b) makes the usbtest driver report errors in the
isochronous bulk transfer tests instead of always returning 0.  As an
arbitrary cutoff, an error is returned if more than 10% of the packet
transfers fail.  It also stops a test immediately upon receiving an URB
submission error.

For a test harness, it's especially important to report when errors occur!

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>