btrfs-progs: check: drop exclusive open mode for --force

The check opens the given device in exclusive by default. In the forced
mode we want to access a device in use, so we have to drop the
exclusivity bit.

This works for block devices but not for files, that could be mounted
via a loop device. In that respect test check/007 is broken and will be
fixed.

Signed-off-by: David Sterba <dsterba@suse.com>

cmds-check.c

@@ -13112,6 +13112,8 @@ int cmd_check(int argc, char **argv)
 			warning(
 			"filesystem mounted, continuing because of --force");
 		}
+		/* A block device is mounted in exclusive mode by kernel */
+		ctree_flags &= ~OPEN_CTREE_EXCLUSIVE;
 	}
 
 	/* only allow partial opening under repair mode */