Set RetailDemoModeService#mDeviceInDemoMode to false

Reset mDeviceInDemoMode when the device exits demo mode. This isn't a
supported configuration in the production devices, but it's used for CTS
in order to run tests back-to-back without reprovisioning the device.

Fixes: 34938521
Test: RetailDemoModeServiceTest
Change-Id: I5a7134815b2817e7b02b1a2df71932faee967e8d

services/retaildemo/java/com/android/server/retaildemo/RetailDemoModeService.java

@@ -541,6 +541,8 @@ public class RetailDemoModeService extends SystemService {
     }
 
     private void stopDemoMode() {
+        mDeviceInDemoMode = false;
+        mIsCarrierDemoMode = false;
         mPreloadAppsInstaller = null;
         mCameraIdsWithFlash = null;
         mInjector.destroyWakeLock();