[bench] create 20 procs & files and write /dev/urandom to them for 4 mins, print out total size

gistfile1.sh

echo; echo -n 'spawning /dev/urandom write procs.. --> '; for i in `seq 0 19`; do  [ -x `cat /dev/urandom > test_file.$i &` ]; echo -n ..$i || echo error spawning $i; done; echo -e '\n\nsleeping 240 seconds'; sleep 240; echo -e '\nkilling procs.\n'; kill -9 `pgrep cat /dev/urandom`; echo -n 'wrote:' && du -h -c test_file* | tail -1

needed to spawn files for read tests with sysbench.