Multi-user and WallpaperColors

Test: set different wallpapers for different users and switch between them.
Test: re-ran cts tests at cts/tests/app/src/android/app/cts/WallpaperManagerTest.java
Change-Id: Ic06d1dc6db26869a2948590863ca9b8ac81c630e
Merged-In: Ic06d1dc6db26869a2948590863ca9b8ac81c630e
Fixes: 63513694