Merge "releasetools: Support generating downgrade A/B OTAs." into nyc-dev am: 5a4508bcef am: e7847765a6 am: a7dcbfb2d8 am: 712bf7d750 am: 6ea73e3566
am: 58bb2216da

Change-Id: Ia76d70e2b7e45739e549537b58f62567305f7faf