Metadata for block apexes can be overridden

Microdroid stores pubkeys from the first boot and uses them to ensure
that block apexes (given from host) is not changed since the last boot.

Microdroid_manager passes pubkeys from the previous boot (stored in
instance.img) to apexd via /apex/vm-payload-metadata.

Bug: 199371341
Test: MicrodroidHostTestCases
Change-Id: Ia361e312279ba3c486e99e679a0eb4e71af86def
2 files changed