update_engine: Use helper Command::AbortWithCustomError() method weaved now provides new variants of Command::Abort() that allow to specify the error information as brillo::Error or binder::Status. Command::AbortWithCustomError(brillo::Error*) also makes sure the error code is prepended with "_", so no need to add that in OnTrackChannel(). BUG: 25875613 Change-Id: Ic9b2cb6f6ef092b85883ebb5bf5e4c936aa770f0