8129597: Add tier 3 test definitions to the JDK 9 forest

Reviewed-by: smarks, jjg
diff --git a/nashorn/test/TEST.groups b/nashorn/test/TEST.groups
index 6f18fa4..aaa6e19 100644
--- a/nashorn/test/TEST.groups
+++ b/nashorn/test/TEST.groups
@@ -27,3 +27,6 @@
 
 # All nashorn tests are tier 2.
 tier2 = src
+
+# No nashorn tests are tier 3.
+tier3 =