LU-137 obdclass: add dt_object_put() and use it

LU-137 obdclass: add dt_object_put() and use it

Introduce dt_object_put() and dt_object_put_nocache() and use them
instead of lu_object_put() and lu_object_put_nocache(), to balance
the use of dt_object_locate() to make a symmetrical interface.

Move the existing ofd_object_put() and osd_object_put() wrappers
into common header functions to use instead of dt_object_put()
or lu_object_put() calls in the respective code, when possible.

Functionally, this patch is a no-op.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I7ef657438441de4a91ee08edb4bc097ac97b7418
Reviewed-on: https://review.whamcloud.com/23092
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>