scsi: ufs: random parallel read and write test

Tests stability on scenarios of multiple threads running random reads
and random writes.
The test introduces the infrastructure for more complex multi-threaded
tests.

Change-Id: I3775f61c65d90d093e4a5b9a9a3e6724f68b5185
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>