LU-9799 mount: Call read_ldd with initialized mount type

LU-9799 mount: Call read_ldd with initialized mount type

When re-reading the ldd when doing relabel, ensure the correct mount
type is used for the read. Otherwise ldiskfs complains:

   mount.lustre FATAL: unhandled/unloaded fs type 0 'ext3'

and ZFS complains:

   e2label: No such file or directory while trying to open MGS/MGT
   Couldn't find valid filesystem superblock.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ife53cff948d545c306e99e4b023989245a1ac3f7
Reviewed-on: https://review.whamcloud.com/28456
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>