LU-15910 llite: enforce ROOT default on subdir mount

LU-15910 llite: enforce ROOT default on subdir mount

In subdirectory mount, the filesystem-wide default LMV doesn't take
effect. This fix includes the following changes:
* enforce the filesystem-wide default LMV on subdirectory mount if
  it's not set separately.
* "lfs getdirstripe -D <subdir_mount>" should print the
  filesystem-wide default LMV.

Add sanity test_413g.

Lustre-change: https://review.whamcloud.com/47518
Lustre-commit: a162e24d2da5e4bd64a79d6dcc128bd0d50e8517

LU-15910 tests: skip sanity/413g for SSK

When running sanity test_413g under review-dne-selinux-ssk-part-1
it intermittently fails.  Temporarily disable this subtest for
this config until the problem is understood and fixed.

Lustre-change: https://review.whamcloud.com/47800
Lustre-commit: TBD (from 8cf4d6ff57dfd51b18997d4b98bf04d008963d70)

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I26de9d02872f0df8918b4ef0765b6b18b84794e6
Reviewed-on: https://review.whamcloud.com/47599
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>