Fix MediaSessionCompatTest failure in SDK<21

MediaSessionImplBase's contructor throws exception due to the missing
mbrComponent, because client test app doesn't declare
MEDIA_BUTTON_RECEIVER in the its manifest.

Fix the test by moving the test to the service test app, which declares
MEDIA_BUTTON_RECEIVER in its manifest.

Test: Run following tests on SDK 16
      $ media/version-compat-tests/runtest.sh 4
Change-Id: Idb5d5cfdbb1593575de319a492bd231b7a567b67
diff --git a/media/version-compat-tests/current/client/src/androidTest/java/android/support/mediacompat/client/MediaSessionCompatTest.java b/media/version-compat-tests/current/service/src/androidTest/java/android/support/mediacompat/service/MediaSessionCompatTest.java
similarity index 94%
rename from media/version-compat-tests/current/client/src/androidTest/java/android/support/mediacompat/client/MediaSessionCompatTest.java
rename to media/version-compat-tests/current/service/src/androidTest/java/android/support/mediacompat/service/MediaSessionCompatTest.java
index c677ea6..b736a5c 100644
--- a/media/version-compat-tests/current/client/src/androidTest/java/android/support/mediacompat/client/MediaSessionCompatTest.java
+++ b/media/version-compat-tests/current/service/src/androidTest/java/android/support/mediacompat/service/MediaSessionCompatTest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2019 The Android Open Source Project
+ * Copyright 2020 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.
@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package android.support.mediacompat.client;
+package android.support.mediacompat.service;
 
 import static org.junit.Assert.assertTrue;