LU-8100 lmv: Correctly generate target_obd

The target_obd proc file was not being generated correctly
in cases where nonconsecutive MDT indices were used when
generating a filesystem.

Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Change-Id: I4bd3aaffd56707ea29b9b2d4366de5e20b3d3760
Reviewed-on: http://review.whamcloud.com/20336
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>