LU-15868 lfsck: don't crash upon dir migration failure

LU-15868 lfsck: don't crash upon dir migration failure

LFSCK against directories that were migrated, but failed may crash,
it's because lost+found directory may not be initialized correctly,
and this error is skipped on purpose, add check in code that
dereference it.

lfsck_verify_lpf() may dereference NULL "child2".

lmv_name_to_stripe_index() should support stripe LMV, which is used
by LFSCK to verify name hash.

Add OBD_FAIL_OUT_EIO to simulate sub transaction failure.

Add sanity-lfsck 15d to verify LFSCK won't crash upon directory
migration failure.

Update sanity-lfsck 4 and 5 to start mds1 with OI scrub enabled, and
wait for mds1 OI scrub finish, otherwise LFSCK may fail to verify
lost+found later.

Lustre-change: https://review.whamcloud.com/47381/
Lustre-commit: 1022e485b5260e3bca0e2acafaf807dffbb02c66 (TBD)

Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity-lfsck env=ONLY=15d,ONLY_REPEAT=100
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I1b1872da2b4ef8f7403effc4d1d3e298c6a0b7e6
Reviewed-on: https://review.whamcloud.com/47620
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>