[ephemeral] auto_update_packages uses PackageResolver

With this change, sysmgr now calls PackageResolver instead of amber
to update a package.

This will allow us to move package fetching decisions from sysmgr to
PackageResolver itself.

CF-230 #comment use PackageResolver for auto_update_packages

TESTED=package_updating_loader_test and manually verified that
auto_update_packages still works

Change-Id: Iec8cad0c37870c011ec9045f11654a10815a5adb
19 files changed