LU-10830 utils: fix create mode for lfs setstripe

LU-10830 utils: fix create mode for lfs setstripe

Fix create mode for files created by "lfs setstripe" and also
"lfs mirror create" to match regular file creates, which are
filtered by umask to determine the final file create mode.

Add test case to verify umask is working correctly in all cases.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I0c9d6730f437dbfbafda4902a035cc0f0ed916b0
Reviewed-on: https://review.whamcloud.com/31747
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>