We should prevent starting home activity before setup

In original call flow, we were using startActivityAsUser, which has
the check, to start home activity.
In previous CL, we replaced it by
mActivityTaskManagerInternal.startHomeOnDisplay but missed the check.
So we need to add it back now.
Also add unit tests.

Bug: 134689126
Test: atest PhoneWindowManagerTests
Change-Id: Icc455d5596f8d9691d61c7b8dda82016720443b7