Explicitly destroy render engine in RenderEngineVts

The GLES driver appears to be left in a bad state without destroying the
render engine instance explicitly after every test case.

Bug: 149043811
Test: build, adb push out/target/product/<platform>/testcases/VtsHalGraphicsComposerV2_2TargetTest/<abi>/VtsHalGraphicsComposerV2_2TargetTest /data/local/tmp && adb shell /data/local/tmp/VtsHalGraphicsComposerV2_2TargetTest
Change-Id: I8e3c4e30eaa2ef3b9831da7b335b9a830be4b4ed