LU-18172: lfsck: umount has to wait lfsck_stop

LU-18172: lfsck: umount has to wait lfsck_stop

When called from umount lfsck_stop() should wait if lfsck is already
stopping. Otherwise, continuation of mdt_fini() or ofd_fini() leads to
various failures. Seen so far:
1.
 osd_scrub_cleanup
   LASSERT(dev->od_otable_it == NULL);
 because lfsck_master_engine() has not reached yet
   oit_iops->fini(env, oit_di)
     osd_otable_it_fini
       dev->od_otable_it = NULL;
2.
 lfsck_find_mdt_idx_by_fid
   rc = fld_server_lookup(env, ss->ss_server_fld...
     BUG: unable to handle kernel NULL pointer dereference
 because ss->ss_server_fld is NULL set on
 mdt_fini
   mdt_fld_fini
     ss->ss_server_fld = NULL;

Test for umount while lfsck is stopping is added.

Test-Parameters: trivial testlist=sanity-lfsck env=ONLY=44
HPE-bug-id: LUS-12421
Signed-off-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Change-Id: I527c071d316ba3405f2199125fa7d018c98c403b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56165
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>