Wi-Fi DPP code refine

1. call Activity#setResult only for RESULT_OK case
2. refine @VisibleForTesting usage
     remove redundant assignment otherwise = PRIVATE
     set all @VisibleForTesting annotated methods package scope
3. rename WifiQrCode#SECURITY_WPA to WifiQrCode#SECURITY_WPA_PSK

Bug: 120645817
Test: atest WifiQrCodeTest
      atest WifiDppConfiguratorActivityTest
      atest WifiDppEnrolleeActivityTest
      atest WifiDppQrCodeGeneratorFragmentTest
      atest WifiDppQrCodeScannerFragmentTest
      atest WifiNetworkListFragmentTest
      atest WifiDppChooseSavedWifiNetworkFragmentTest

Change-Id: Id5de7eadc73185716422fc0d197f82bdd025ce45

src/com/android/settings/wifi/dpp/WifiDppChooseSavedWifiNetworkFragment.java

@@ -17,7 +17,6 @@
 package com.android.settings.wifi.dpp;
 
 import android.app.ActionBar;
-import android.app.Activity;
 import android.app.settings.SettingsEnums;
 import android.content.Intent;
 import android.os.Bundle;
@@ -100,9 +99,7 @@ public class WifiDppChooseSavedWifiNetworkFragment extends WifiDppQrCodeBaseFrag
                     .ACTION_CONFIGURATOR_QR_CODE_GENERATOR.equals(action)) {
                 getFragmentManager().popBackStack();
             } else {
-                final Activity activity = getActivity();
-                activity.setResult(Activity.RESULT_CANCELED);
-                activity.finish();
+                getActivity().finish();
             }
         });