Update the system API to support multi client RoR

Detailed design in http://go/multi-client-ror. We will reuse most of
the old APIs, and there are a few notable changes
1. Infer the package name from the existing context
2. Remove the unused update token
3. Add the REBOOT permission, so phonesky can hold it.
4. Add a new API for rebootAndApply, which takes a slotSwitch parameter

Bug: 170664917
Test: build

Change-Id: Icb012138bd1789ce03564aa255e5bd4e84374130