LU-10465 lov: decrease default stripe size to 1MB

LU-10465 lov: decrease default stripe size to 1MB

Commit 3f5abc6fa30e7c0256077ccf6a149d1809450465 increased
the default stripe size from 1MB to 4MB. However, this
caused usability issue in LU-10786 for PFL/DoM files.

This patch changes the default stripe size back to 1MB
until we have a better method of handling DoM components.
Otherwise, it means that DoM files will not be created
easily with default settings.

Change-Id: Ie6b6fe97596ed65abec771b3f37afd950dc821c8
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: https://review.whamcloud.com/31589
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>