8185458: Added comment for Files.notExists in FileUtils test library

Reviewed-by: chegar
diff --git a/test/lib/jdk/test/lib/util/FileUtils.java b/test/lib/jdk/test/lib/util/FileUtils.java
index a5e1777..9250128 100644
--- a/test/lib/jdk/test/lib/util/FileUtils.java
+++ b/test/lib/jdk/test/lib/util/FileUtils.java
@@ -98,6 +98,7 @@
         while (true) {
             try {
                 Files.delete(path);
+                // Checks for absence of the file. Semantics of Files.exists() is not the same.
                 while (!Files.notExists(path)) {
                     times++;
                     if (times > MAX_RETRY_DELETE_TIMES) {