Gracefully fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails

This is as reported at - https://mail.openjdk.java.net/pipermail/lanai-dev/2020-December/000789.html

On macOS 10.12, Lanai JDK fails at the runtime if user asks for Metal rendering pipeline using VM option -Dsun.java2d.metal=true.
We don't expect Metal to run on this version (macOS 10.12), but the runtime failure should be fixed by providing a log message and gracefully falling back to the OpenGL rendering pipeline.