LU-12530 utils: narrow l_tunedisk udev rule

Narrow the udev rule so that it runs l_tunedisk only for ext4 block
devices formatted for Lustre.

Devices which are members of ZFS pools do not need such tunings to
be provided by lustre - they are handled by ZFS.

There are currently no other OSD types in the tree.  Sites/Vendors which
support other OSDs will need to adjust the rule appropriately.

Change-Id: Iba8b20fc705da0259ab71ee33b92193cae7e8eae
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-on: https://review.whamcloud.com/36599
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>