test-texture-async: Clean up the test code
test-texture-async: Clean up the test code

Force threading on, and stop using the default stage and behaviours:
let's try to use modern API.

jigpu/clutter,djdeath/clutter-multithreaded,djdeath/clutter,ebassi/clutter,heysion/clutter-clone,djdeath/clutter-android,djdeath/clutter-android,Distrotech/clutter,heysion/clutter-clone,collects/clutter,djdeath/clutter,jigpu/clutter,djdeath/clutter,heysion/clutter-clone,jigpu/clutter,GNOME/clutter,heysion/clutter-clone,GNOME/clutter,collects/clutter,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter,djdeath/clutter-android,jigpu/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,kerrickstaley/clutter-vala,ebassi/clutter,GNOME/clutter,djdeath/clutter,jigpu/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,Distrotech/clutter,kerrickstaley/clutter-vala,GNOME/clutter,GNOME/clutter,ebassi/clutter,Distrotech/clutter,collects/clutter,kerrickstaley/clutter-vala,heysion/clutter-clone,ebassi/clutter,collects/clutter,djdeath/clutter-android,ebassi/clutter,Distrotech/clutter,collects/clutter