[Test] Ignore missing suites

Ignore bundles for which no test suites have been defined.
Used to support development of framework layer (don't
stall the test runner just because some bundle does not
have defined tests yet), WTD-518.

test.html

@@ -50,7 +50,12 @@
                     xhr.open("GET", file);
                     xhr.onreadystatechange = function () {
                         if (xhr.readyState === 4) { // DONE
-                            callback(JSON.parse(xhr.response));
+                            if (xhr.status === 200) {
+                                callback(JSON.parse(xhr.response));
+                            } else {
+                                // No suite defined, so no tests
+                                callback([]);
+                            }
                         }
                     }
                     xhr.send();