LU-11913 utils: allow "mq-deadline" as scheduler

LU-11913 utils: allow "mq-deadline" as scheduler

Allow the "mq-deadline" scheduler for multi-queue block devices, in
addition to just "noop" and "deadline".  Explicitly add "deadline"
as a valid option, in case the default scheduler is changed.

Lustre-change: https://review.whamcloud.com/34163
Lustre-commit: 4326ab53b7142e474c75b46da2361d148a2f7ce8

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I2cb0878188aea43f88c503ea70a699be083ebbe5
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/34426
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>