overlay: correct scratch dirs check

Tests that use _overlay_scratch_mount_dirs instead of _scratch_mount
should use _require_scratch_nocheck instead of _require_scratch
because these tests are either mounting with multiple lower dirs or
mounting with non-default lower/upper/work dir, so
_check_overlay_scratch_fs won't handle these cases correctly. So we
introduce _overlay_check_scratch_dirs helper and should call this
helper with the correct dir arguments for these non-default cases.

This patch modify these tests to optionally call
_overlay_check_scratch_dirs at the end of the test or after
_scratch_umount to mount base filesystem only and run the checker.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/overlay/055

@@ -67,8 +67,10 @@ _cleanup()
 _supported_fs overlay
 _supported_os Linux
 _require_test
-_require_scratch
 _require_test_program "open_by_handle"
+# Use non-default scratch underlying overlay dirs, we need to check
+# them explicity after test.
+_require_scratch_nocheck
 # We need to require all features together, because nfs_export cannot
 # be enabled when index is disabled
 _require_scratch_overlay_features index nfs_export redirect_dir
@@ -122,10 +124,14 @@ mount_dirs()
 				-o "index=on,nfs_export=on,redirect_dir=on"
 }
 
-# Unmount the overlay without unmounting base fs
+# Unmount the overlay without unmounting base fs and check the
+# underlying dirs
 unmount_dirs()
 {
 	$UMOUNT_PROG $SCRATCH_MNT
+
+	_overlay_check_scratch_dirs $middle:$lower $upper $work \
+				-o "index=on,nfs_export=on,redirect_dir=on"
 }
 
 # Check file handles of dir with ancestor under lower redirect