EX-6808 tests: allow run_lfsck() to skip error

EX-6808 tests: allow run_lfsck() to skip error

If e2fsck or lfsck are repairing any corruption it means
the filesystem was corrupted by something, and that
shouldn't happen during testing. Running run_lfsck() will
fail and report an error.

However, after running sanityn test 70b, there will be
some known corruptions need to be repaired. We have to
make run_lfsck() support skipping some allowed errors
so as to make sanity-lipe-find3 and sanity-lipe-find3
tests proceed.

Test-Parameters: trivial testlist=sanityn,sanity-lipe-scan3
Test-Parameters: trivial testlist=sanityn,sanity-lipe-find3
Test-Parameters: trivial mdscount=2 mdtcount=4 \
testlist=sanityn,sanity-lipe-scan3
Test-Parameters: trivial mdscount=2 mdtcount=4 \
env=SANITY_LIPE_FIND3_EXCEPT=109 \
testlist=sanityn,sanity-lipe-find3

Fixes: f9ba28af02 ("EX-6692 tests: run LFSCK in sanity-lipe-scan3/find3")
Change-Id: I686820a70b1a393611d90e286febfd3512fd40f7
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49903
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>