MicrodroidTestApp is a helper app

MicrodroidTestApp shouldn't be installed in system/app but sometimes
this happens and MicrodroidHostTestCases fails.

Changing the module type to android_test_helper_app, it won't be
installed in /system/app.

Bug: 193134988
Test: MicrodroidHostTestCases
Change-Id: I97647d1f2cd9f2f5b7c19121fbf98b244a4b5a3b
diff --git a/tests/testapk/Android.bp b/tests/testapk/Android.bp
index f14fca8..7332149 100644
--- a/tests/testapk/Android.bp
+++ b/tests/testapk/Android.bp
@@ -2,7 +2,7 @@
     default_applicable_licenses: ["Android-Apache-2.0"],
 }
 
-android_app {
+android_test_helper_app {
     name: "MicrodroidTestApp",
     srcs: ["src/java/**/*.java"],
     libs: [