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

Change-Id: I79f8ed59d9011f84ccf71e1c30e7cdce6c2afd26