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/WifiDppEnrolleeActivity.java

@@ -117,7 +117,6 @@ public class WifiDppEnrolleeActivity extends InstrumentedActivity implements
                 break;
             default:
                 Log.e(TAG, "Launch with an invalid action");
-                setResult(Activity.RESULT_CANCELED);
                 finish();
         }
     }
@@ -141,7 +140,6 @@ public class WifiDppEnrolleeActivity extends InstrumentedActivity implements
 
     @Override
     public boolean onNavigateUp(){
-        setResult(Activity.RESULT_CANCELED);
         finish();
         return true;
     }