Added Macros for RENDERTHREAD_TESTS which run these tests using specific backends.
RENDERTHREAD_TESTS - Runs OpenGL, SkiaGL, and SkiaVulkan
RENDERTHREAD_SKIA_TESTS - Runs SkiaGL and SkiaVulkan
RENDERTHREAD_OPENGL_TESTS - Runs OpenGL
Test: manual running of hwui_unit_tests
Change-Id: Ia7420ee7a38803a15e2d58394d14b38cae8208d3