writecache: fix test flush on moving to degraded mode

Although there is `ignoreErrors` flag, but when `flushObjects` occurs in
FSTree, the error should be returned as with Bolt.

Signed-off-by: Andrey Butusov <[email protected]>

Author: End-rey

pkg/local_object_storage/writecache/flush.go

@@ -207,9 +207,6 @@ func (c *cache) flushFSTree(ignoreErrors bool) error {
 
 		err = c.flushObject(&obj, data)
 		if err != nil {
-			if ignoreErrors {
-				return nil
-			}
 			return err
 		}