Supporting change for aosp/771168

Submitting the change above before this one will "work" for now but we
want to pass vbmeta.img instead of system.img for the more robust
solution.

Bug: 78113934
Test: Built on my local machine.  Asserted that VerifiedBootParams.proto
exists.  Asserted that the emulator boots correctly with this file.

Change-Id: Ie91f49a3c7d49fc667e3f12e7e3866c3d9eb1960