Send onUnlockUser() before PRE_BOOT broadcasts.

Before this change, a PRE_BOOT_COMPLETED receiver could try calling
back into the system to ask for AccountManager details, only to be
told the user wasn't unlocked yet.  If the broadcast code was probing
in a loop, it would force us to wait around for the 60-second ANR
timeout.  Since typical devices have ~7 PRE_BOOT receivers, this
would delay BOOT_COMPLETED and other operations, like mounting the
SD card, for up to 7 minutes.

Bug: 28024024

Change-Id: Ibf8611e6fe94b0deb5ae5715c86f897ff6779088