Enable app launch test: "app replaces wallpaper"

This test was previously disabled because it was not compatible with the app rotation animation changes. This CL re-enables the test.

 To check if the app launches correctly the flicker tests check:
 (1) background layer is visible in the beginning
 (2) app layer replaces background layer
 (3) once shown, app layer is always visible

Test: atest FlickerTests:OpenAppWarmTest and atest FlickerTests:OpenAppColdTest
Change-Id: I08fab7c5efd7aa0307ac4d058b4759688e568e10