Auto generate test config files

This change allows one to run atest <module name>. The TradeFed test
config file will be automatically created in testcases directory based
on the settings.

Bug: 69929803, 69932044
Test: m -j NotificationStressTests libminijail_test
add following lines in notificationtests/Android.mk,
before "include $(BUILD_PACKAGE)"
LOCAL_COMPATIBILITY_SUITE := general-test

Change-Id: Ib5e9cd152d957b5d5beb6ed23a899a021a7e06d6
diff --git a/core/empty_test_config.xml b/core/empty_test_config.xml
new file mode 100644
index 0000000..7c9daff
--- /dev/null
+++ b/core/empty_test_config.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2017 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+<!-- No AndroidTest.xml was provided and the manifest does not include
+     instrumentation, hence this apk is not instrumentable.
+-->
+<configuration description="Empty Configuration" />