Clearing reader and writer queues in executeCommands for HWC VTS Tests

Test: ./VtsHalGraphicsComposerV2_1TargetTest,
./VtsHalGraphicsComposerV2_2TargetTest

Change-Id: Ie47e486d191da30be47cde47d768d3cdde8e04e9
diff --git a/graphics/composer/2.1/utils/vts/ComposerVts.cpp b/graphics/composer/2.1/utils/vts/ComposerVts.cpp
index 1cafafe..250c392 100644
--- a/graphics/composer/2.1/utils/vts/ComposerVts.cpp
+++ b/graphics/composer/2.1/utils/vts/ComposerVts.cpp
@@ -311,6 +311,8 @@
                                  ASSERT_TRUE(reader->readQueue(tmpOutLength, tmpOutHandles));
                                  reader->parse();
                              });
+    reader->reset();
+    writer->reset();
 }
 
 }  // namespace vts