Slices feature supports device model.

- Migrate DeviceModelPreferenceController to BasePreferenceController
- Because Slice feature enables strict mode,
  we can't do I/O(DeviceInfoUtils.getMsvSuffix) on main thread.

  Using FutureTask to get around the foreground thread restriction.

- Modify test case for new device model controller.

Test: slice uri > content://android.settings.slices/intent/my_device_model
Test: make RunSettingsRoboTests -j
      atest UniquePreferenceTest SettingsGatewayTest

Change-Id: Idafc132dfa14138ad5a7edd58e63c4b0f644c994