scsi: ufs: add check_completion_fn to long_sequential unit test

This patch adds a completion condition to the long sequential unit test.
The condition is the completion of ALL the requests that where created.
Before this condition, the calculated test throughput was not accurate
since the transfered size was not constant.
This patch also increases the request size to the maximum - 128 bios.
In addition, the calculated throughput is always printed to the log.

Change-Id: Ibc16dc60486ff2b58cbc8ce02aee2ad87fea7ba1
Signed-off-by: Lee Susman <lsusman@codeaurora.org>