Read all blocks in system and vendor partition during boot time
so that dm-verity could verify this partition is properly flashed.
Bug: 27175949
Change-Id: I38ff7b18ee4f2733e639b89633d36f5ed551c989
update_verifier checks the integrity of the updated system and vendor
partitions on the first boot post an A/B OTA update. It marks the
current slot as having booted successfully if it passes the verification.
This CL doesn't perform any actual verification work which will be
addressed in follow-up CLs.
Bug: 26039641
Change-Id: Ia5504ed25b799b48b5886c2fc68073a360127f42