fs-bench: rename test*.sh scripts to fs-bench-test*.sh

Install name of these scripts is in conflict with testcases/lib/test.sh.
In problem Awais reported, he ended up with test.sh from fs-bench in
install directory, instead of shell script library he was expecting:
  install -m 00775 "/root/ltp/testcases/lib/test.sh" "/opt/ltp/testcases/bin/test.sh"
  ...
  install -m 00775 "/root/ltp/testcases/kernel/fs/fs-bench/test.sh" "/opt/ltp/testcases/bin/test.sh"

Reported-by: Awais Belal <Awais_Belal@mentor.com>
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>