Change app selection policy for post-OTA verification

Changes the policy for selecting packages which will be pre-verified
during post-OTA boot animation.

For Nx to Ny, an app is pre-verified if used in the foreground in the
last 7 days, or if its APK was loaded by other apps.

For M to N (or early N builds without detailed stats), an app is
pre-verified if it has any recorded use in the last 7 days.

Bug: 27902702
Bug: 27350503
Change-Id: I2b38daf017ecd0e5aa5ed596ed9351cffa03dbcb