qt: Treat regtest as testnet

No need to do anything special in the GUI for regtest mode,
but do treat it at testnet not mainnet to prevent confusion.

src/qt/clientmodel.cpp

@@ -123,9 +123,12 @@ void ClientModel::updateAlert(const QString &hash, int status)
     emit alertsChanged(getStatusBarWarnings());
 }
 
-bool ClientModel::isTestNet() const
+QString ClientModel::getNetworkName() const
 {
-    return TestNet();
+    QString netname(QString::fromStdString(Params().DataDir()));
+    if(netname.isEmpty())
+        netname = "main";
+    return netname;
 }
 
 bool ClientModel::inInitialBlockDownload() const