conform: Move timeline-base under conditional check
conform: Move timeline-base under conditional check

The timeline base test unit is pretty slow, and under heavy load it will
tend to fail because of skipped frames. We should put it under
conditional testing and only run it if `-m slow` is passed to the test
harness.

jigpu/clutter,djdeath/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,jigpu/clutter,GNOME/clutter,Distrotech/clutter,djdeath/clutter,GNOME/clutter,Distrotech/clutter,GNOME/clutter,ebassi/clutter,jigpu/clutter,Distrotech/clutter,djdeath/clutter,GNOME/clutter,ebassi/clutter,ebassi/clutter,djdeath/clutter,Distrotech/clutter,ebassi/clutter,ebassi/clutter,djdeath/clutter,jigpu/clutter,Distrotech/clutter