[flexiglass] Fixes SceneContainerStartableTest

The reason this was broken on head was because
Flags.SCENE_CONTAINER_ENABLED was false, failing the assumption in
SceneContainerStartableTest and skipping the test.

After setting Flags.SCENE_CONTAINER_ENABLED to true, two methods in the
test were failing, both having to do with the device wakefulness
model/state. I haven't looked into what caused this regression.

The CL fixes the issue by updating the test.

Fix: 305062590
Test: N/A this is a test fix
Flag: scene_container
Change-Id: I48acb03d281b0e78ac6c7decda6fb82eba019fa3