Wait for ASECs to be scanned before proceeding

Move MountService up the list, then pause waiting for MountService to
finish scanning ASECs before the services that require those packages to
be ready.

Additionally, don't automatically mark all ASEC apps as FLAG_EXTERNAL on
reboot. This prevents AppWidgets and other things from being used with
ASECs which are on internal storage.

Bug: 6445613
Change-Id: I3e0b3e244fec966814d7a5ea93de5d337aea79bd