ZFS already sets elevator=noop for wholedisk vdevs (for all pools), but
typical root-on-ZFS installations use partitions. This sets
elevator=noop on the disks in the root pool.
Ubuntu 16.04 and 16.10 had this. It was lost in 17.04 due to Debian
switching to this upstream initramfs script.
Signed-off-by: Richard Laager <rlaager@wiktel.com>
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