LU-4109 tests: raise out-of inode LOV EA detection threshold

LU-4109 tests: raise out-of inode LOV EA detection threshold

Sanity sub-test 57b sometimes failed because the threshold (< 8K
of MDT space) it used to detect if LOV EA has been stored out-of
inode is too short (vs space also allocated for llog files, ChangeLog,
etc). So raising threshold to 16.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I0f59328d59da69911473433769ff683ff4fdf452
Reviewed-on: http://review.whamcloud.com/8156
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>