Installing packages to expanded storage.

PackageManager now offers to load/unload packages when expanded
volumes are mounted/unmounted.  Expanded storage volumes are still
treated as FLAG_EXTERNAL_STORAGE from a public API point-of-view,
but this change starts treating the INSTALL_EXTERNAL flag as
exclusively meaning ASEC containers.

Start tracking the UUID of the volume where a package is installed,
giving us a quick way to find relevant packages.  When resolving an
install location, look across all expanded volumes and pick the one
with the largest free space.  When upgrading an existing package,
continue preferring the existing volume.  PackageInstaller now knows
how to stage on these volumes.

Add new movePackage() variant that accepts a target volume UUID
as destination, it will eventually move data too.  Expose this
move command through "pm" command for testing.

Automount expanded volumes when they appear.

Bug: 19993667
Change-Id: I9ca2aa328b9977d34e8b3e153db4bea8b8d6f8e3