LU-13748 mdt: remove LASSERT in mdt_dump_lmm()

LU-13748 mdt: remove LASSERT in mdt_dump_lmm()

Change LASSERT() in mdt_dump_lmm() into a CERROR(), since this
function is normally used for debugging and it doesn't help to
crash the MDS just when it complaining about some file layout.

Add sanity test_27Cg that triggered this initially.

Lustre-change: https://review.whamcloud.com/50532
Lustre-commit: 97d29eb800e8d9faba04f0744376cb50b239e2e9

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I27f0b4489de48d6f197e0143589d76428d85e549
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52728
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>