LU-15738 test: check lfsck status before starting

LU-15738 test: check lfsck status before starting

If the LFSCK has been started before calling "lfsck_start"
to start it, the test shouldn't fail for starting LFSCK.

Lustre-change: https://review.whamcloud.com/48018/
Lustre-commit: 29aaf679afac89359e1b116b8de0480f24b4e8ac

Test-Parameters: trivial testlist=sanity-lfsck
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Change-Id: I266d9e2b9c5f37eb9e08b489fab428268b90d895
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48841
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>