Observe new apexd status value of "activated" as required.

As of aosp/1224611, there is a new step in the preparation of APEXes
where init calls back into apexd after DE user data is unencrypted to
allow DE apex data to be snapshotted or restored.

aosp/1228581 introduces a new apexd.status value of "activated" that
is set once APEXes are activated but before this snapshot has occurred.

init may execute "perform_apex_config" once this has occurred, so this
CL changes init to wait for "activated" rather than "ready" before
doing this.

Bug: 148672144
Test: build & flash, check boot completes and check in logs that init
waits on the correct status value.

Change-Id: I339580bf593d3b09a5dff749ac2a5d1952bcb210