scsi: ufs: long sequential read/write tests

This test adds the ability to test the UFS task management feature
in the driver. It loads the queue with requests in order to allow
the task management to operate in full capacity.

Modify test-iosched infrastructure to support the new tests:
- expose  check_test_completion()

Note: we submit 16-bio requests since the current HW is very slow
and we don't want to exceed the timeout duration.

Change-Id: I8ee752cba3c6838d8edc05747fa0288c4b347ef6
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
Signed-off-by: Lee Susman <lsusman@codeaurora.org>