ITS: test_scene_change refactor

Recent changes in supported phones 3A behavior allows larger
test base. This refactor is based on testing 5 cameras instead of
just 1 camera.

Refactor includes:
  Opening cam object 1 time at beginning and keeping it open.
  Changing timing shifts larger for no change during capture
  Handling scene changes during 3A settling better

bug: 150867542

Change-Id: I6bc5953366e739e9d5daa0864c6c67e8ef42833c