LU-13168 tests: verify truncated xattr is handled

LU-13168 tests: verify truncated xattr is handled

Verify that a truncated trusted.lov xattr is handled properly,
for both plain and PFL layouts.

Add a test case that verifies this is fixed for both layout types.

Lustre-change: https://review.whamcloud.com/38434
Lustre-commit: cb74546354201434a6fd3d53acd1a0808fbfcb1c

Fixes: f2d06d3c76 ("LU-12911 llite: Don't access lov_md fields before size check")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I11d420c7fdc2362f64689a545b95c76e893ebbe5
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/38604
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>