DO NOT MERGE: improve TestVirtualDisplayRecycles to reduce memory usage

TestVirtualDisplayRecycles allocates lots of memory.
in low memory system, this test get failed because
android.media.cts process died by low-memory killer easily.

To prevent low memory case during test,
- clear the allocated buffer for dalvik to get more chance
  to do GC at window cleanup
- call cleanupGl() at stopComposition

Change-Id: I1c118ceba9dfe29a84bd9edad43eac21ba50a92b
Signed-off-by: Harry Hong <hhong@nvidia.com>
(cherry picked from commit caf25cf58f45c3c2039de16d37242deab0e45c57)
(cherry picked from commit 1c01e9d1bb4724b983e9d756ce7238a162f9f7a2)
diff --git a/tests/tests/media/src/android/media/cts/EncodeVirtualDisplayWithCompositionTest.java b/tests/tests/media/src/android/media/cts/EncodeVirtualDisplayWithCompositionTest.java
index 89d6efa..014c1a5 100644
--- a/tests/tests/media/src/android/media/cts/EncodeVirtualDisplayWithCompositionTest.java
+++ b/tests/tests/media/src/android/media/cts/EncodeVirtualDisplayWithCompositionTest.java
@@ -657,6 +657,7 @@
             } catch (InterruptedException e) {
                 // don't care
             }
+            cleanupGl();
             mCompositionThread = null;
             mSurface = null;
             mStartCompletionSemaphore = null;
@@ -966,6 +967,7 @@
 
             public void cleanup() {
                 mNumTextureUpdated.set(0);
+                mVerticesData.clear();
                 if (mTextureId != 0) {
                     int[] textures = new int[] {
                             mTextureId