LU-15307 lod: add option to set max dir stripe count

LU-15307 lod: add option to set max dir stripe count

Add an option to limit max dir stripe count when the default
dir stripe count is set to -1.

Signed-off-by: Lei Feng <flei@whamcloud.com>
Change-Id: I12dd5be15012a28bda30da85f24bc726c37f1ac7
Reviewed-on: https://review.whamcloud.com/45724
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>