Route Internet test function to main app.

Switch test from 8.8.8.8:53 to "www.github.com:80"

src/QGCApplication.cc

@@ -668,3 +668,8 @@ void QGCApplication::qmlAttemptWindowClose(void)
 {
     QMetaObject::invokeMethod(_rootQmlObject(), "attemptWindowClose");
 }
+
+bool QGCApplication::isInternetAvailable()
+{
+    return getQGCMapEngine()->isInternetActive();
+}

src/QGCApplication.h

@@ -92,6 +92,9 @@ public:
     /// Do we have Bluetooth Support?
     bool isBluetoothAvailable() { return _bluetoothAvailable; }
 
+    /// Is Internet available?
+    bool isInternetAvailable();
+
 public slots:
     /// You can connect to this slot to show an information message box from a different thread.
     void informationMessageBoxOnMainThread(const QString& title, const QString& msg);

src/QtLocationPlugin/QGCTileCacheWorker.cpp

@@ -1056,7 +1056,7 @@ void
 QGCCacheWorker::_testInternet()
 {
     QTcpSocket socket;
-    socket.connectToHost("8.8.8.8", 53);
+    socket.connectToHost("www.github.com", 80);
     if (socket.waitForConnected(2500)) {
         qCDebug(QGCTileCacheLog) << "Yes Internet Access";
         emit internetStatus(true);