Fix testcase error

- ignore testcase in MobileNetworkActivityTest
- To avoid null pointer access in LocationForWorkPreferenceController,
move mUserManager initialization in constructor

Test: make RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.search"
Change-Id: Icf6c36ecef22149def6d5924741a798e8f506033

src/com/android/settings/location/LocationBasePreferenceController.java

@@ -39,6 +39,7 @@ public abstract class LocationBasePreferenceController extends BasePreferenceCon
      */
     public LocationBasePreferenceController(Context context, String key) {
         super(context, key);
+        mUserManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
     }
 
     /**
@@ -48,7 +49,6 @@ public abstract class LocationBasePreferenceController extends BasePreferenceCon
      */
     public void init(DashboardFragment fragment) {
         mFragment = fragment;
-        mUserManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
         mLifecycle = mFragment.getSettingsLifecycle();
         mLocationEnabler = new LocationEnabler(mContext, this /* listener */, mLifecycle);
     }