Don't touch system_ce until the first user unlock.

This CL does the following things:
1) Only start PersistQueue when the first user unlocked.
2) Only create recent task folder when we need to write the first file
to it.

Bug: 124697664
Test: Manual test -- checked recent_tasks, recent_images and
launch_params folders are still created correctly. No encryption policy
log seen.
Change-Id: I5b8bf712a3c45092b463622731d58f90d76fec58