LU-8100 tests: Test the correctness of target_obd

The target_obd proc file is what is used by lfs to list mdts
of a lustre file system. Added a conf-sanity test to ensure
correctness of lfs mdts output.

Test-Parameters: trivial mdtfilesystemtype=ldiskfs mdsfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs mdtcount=1 testlist=conf-sanity
Test-Parameters: trivial mdtfilesystemtype=ldiskfs mdsfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs mdtcount=2 mdtcount=4 testlist=conf-sanity
Test-Parameters: trivial mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs mdtcount=1 testlist=conf-sanity

Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Change-Id: Ia876ed456b95570b90bc90f05d8b7b97e1aa71af
Reviewed-on: http://review.whamcloud.com/20546
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>