block: test-iosched: disable statistic flag on request

The flag REQ_IO_STAT is enabled by default this assumes statistics are
initialized and might cause NULL references in the kernel. To avoid it
this flag is cleared in the request and stats are not updated.

Change-Id: I6a1890dde51dfa8ffdd376b13f4466c9db0ae05b
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>