Fix initial notification icon visibility

AOD shelf should start hidden, and only become visible once the device
enters doze mode.

Test: visual
Fixes: 150729343
Change-Id: I7d58ca8113701616b0e3a7f768311f813c2fce4f

packages/SystemUI/res-keyguard/layout/keyguard_status_view.xml

@@ -75,6 +75,7 @@
             android:layout_width="match_parent"
             android:layout_height="@dimen/notification_shelf_height"
             android:layout_marginTop="@dimen/widget_vertical_padding"
+            android:visibility="invisible"
         />
     </LinearLayout>
 </com.android.keyguard.KeyguardStatusView>