Merge changes from topic "oms-transactional-api"

* changes:
  OMS: add tests for the OMS transactional API
  Push OverlayDeviceTests onto /system
  OMS: add transactional API
  OMS: block until settings are persisted
  OMS: replace OMSImpl.OverlayChangeListener with return values
  OverlayDeviceTests: add missing TEST_MAPPING