LU-5814 lov: use obd_get_info() to get def/max LOV EA sizes

LU-5814 lov: use obd_get_info() to get def/max LOV EA sizes

Use obd_get_info() to get the default and maximum LOV EA sizes (along
with maximum cookiesize) from LOV. Remove the then unused function
obd_size_diskmd() and the unused get info key KEY_LOVDESC. When
computing the maximum LOV EA size use the active OST count
(ld_active_tgt_count) rather than the OST count (ld_tgt_count).

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I4a7eb158d9cb8f4828f5cb272df8d1c843f2eb6b
Reviewed-on: http://review.whamcloud.com/13695
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>