ITS: refactor test_exposure.py

1. Move RAW plot in debug before RGB. If RBG fails, RAW never plots.
   One mainly wants RAW when RGB has failed.
2. Change color for 'GB' in raw plot to black.
3. Refactor 'assert something --> if not something: raise AssertionError'

bug: 184561023, 187513164
Change-Id: Ia7e3713789cc50ad5d4aa91071e2a12168b28190
1 file changed