Skip swiftshader tests based on active GPU Currently Swiftshader tests are skipped only if a swiftshader device is requested. We should also skip swiftshader tests if the default GPU on the system is swiftshader, as is the case in certain emulated systems. Bug: angleproject:4626 Change-Id: I3ee83c43d35eb4f94b516e80689b241d53bbfb62 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2192090 Commit-Queue: Michael Spang <spang@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>