Add Java 1.9.0 release to client_matrix.py

tools/interop_matrix/client_matrix.py

@@ -132,6 +132,9 @@ LANG_RELEASE_MATRIX = {
         {
             'v1.8.0': None
         },
+        {
+            'v1.9.0': None
+        },
     ],
     'python': [
         {