Clean up KeyStore exception warning caused by adding a new VPN.

Bug:109791294
Test: manually navigate to settings and click the + button in VPN.
Change-Id: Ib94778ef3fdab0fc8147477b91f644c54dc04c24

src/com/android/settings/vpn2/VpnUtils.java

@@ -38,7 +38,8 @@ public class VpnUtils {
     private static final String TAG = "VpnUtils";
 
     public static String getLockdownVpn() {
-        final byte[] value = KeyStore.getInstance().get(Credentials.LOCKDOWN_VPN);
+        final byte[] value = KeyStore.getInstance().get(
+            Credentials.LOCKDOWN_VPN, true /* suppressKeyNotFoundWarning */);
         return value == null ? null : new String(value);
     }