LU-4165 tests: restore skipped sanity-lfsck tests

LU-4165 tests: restore skipped sanity-lfsck tests

Many subtests in sanity-lfsck were incorrectly being skipped due
to a cleanup patch that was intended to skip those tests for very
old Lustre versions being run on the MDS, or for ZFS MDTs.

Instead, a large number of tests were *always* being skipped.

Restore those accidentally-skipped tests.  Hopefully they still pass.

Clean up code style for the script:
- remove the needless "return" after "skip"
- use mds1_FSTYPE and MDS1_VERSION instead of getting values from MDS

Fixes: c54b6ca2bdb ("LU-13718 tests: add LU numbers to skipped tests")
Test-Parameters: trivial fstype=ldiskfs testlist=sanity-lfsck
Test-Parameters: fstype=ldiskfs mdscount=2 mdtcount=4 testlist=sanity-lfsck
Test-Parameters: fstype=zfs testlist=sanity-lfsck
Test-Parameters: fstype=zfs mdscount=2 mdtcount=4 testlist=sanity-lfsck
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I4e49d79826369a546576672f77f7012f4a3ebbe5
Reviewed-on: https://review.whamcloud.com/40760
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>