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.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I2cb0878188aea43f88c503ea70a699be083ebbe5
Reviewed-on: https://review.whamcloud.com/34163
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>