LU-12387 utils: Read existing ldd data in l_tunedisk

LU-12387 utils: Read existing ldd data in l_tunedisk

Read the lustre_disk_data from the device passed to l_tunedisk, so
we can determine whether the device is an MGT or MDT and thus skip
the tuning of the device.

Fixes: 892280742a2b ("LU-9551 utils: add l_tunedisk to fix disk tunings")
Fixes: 2f8d7b4679de ("LU-11736 utils: don't set max_sectors_kb on MDT/MGT")
Cray-bug-id: LUS-7358
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: I193fe008d5777b0e83f2be9a500eaffb1d3ca615
Reviewed-on: https://review.whamcloud.com/35066
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>