LU-4134 obdclass: obd_device improvement

LU-4134 obdclass: obd_device improvement

The patch removes self exports from obd's reference counting which
allows to avoid freeing of self exports by zombie thread.
A pair of functions class_register_device()/class_unregister_device()
is to make sure that an obd can not be referenced again once its
refcount reached 0. For target_handle_connect() take a reference for
obd_device during finding it by name.

Fix grant mismatch message
	"tot_granted 4194304 != fo_tot_granted".

Signed-off-by: Vladimir Saveliev <vladimir.saveliev@seagate.com>
Signed-off-by: Alexey Lyashkov <alexey.lyashkov@seagate.com>
Signed-off-by: Alexander Boyko <alexander.boyko@seagate.com>
Seagate-bug-id: MRP-2139 MRP-3267
Change-Id: I9cc6860431c6bb7db6983e0d15a5d3d2b564265e
Reviewed-on: https://review.whamcloud.com/8045
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>