tests/block/014: ignore dd error messages

The kernel commit de3510e52b0a ("null_blk: fix command timeout
completion handling") fixed null_blk driver to report ETIMEDOUT errors
for IO operations failed with a timeout. This change causes the dd call
in block/014 case to print the following error message:

dd: error reading '/dev/nullb0': Connection timed out

The presence of this message result in a failure of the test case even
without a kernel crash or hang, which is what the block/014 case is
testing. Avoid this failure by ignoring dd error messages using a
redirection of dd stderr to /dev/null.

Reported-by: kernel test robot <[email protected]>
Signed-off-by: Damien Le Moal <[email protected]>

Author: damien-lemoal

tests/block/014

@@ -34,7 +34,7 @@ test() {
 		# crash or hang.
 		for ((i = 0; i < 100; i++)); do
 			dd if=/dev/nullb0 of=/dev/null bs=4K count=4 \
-				iflag=direct status=none &
+				iflag=direct status=none > /dev/null 2>&1 &
 		done
 		wait
 	done