Look for non-empty responses instead of the string "OK"

Only litelib_initialize_xxx functions return OK to say that the connection worked,
others return actual JSON.

src/connection.cpp

@@ -368,7 +368,8 @@ void Executor::run()
         DEBUG("ignoring exception: " << e.what() );
     }
 
-    if (response.toUpper().trimmed() != "OK") {
+    //TODO: we can do stricter error checking
+    if (response.isEmpty()) {
         config->server = Settings::getRandomServer();
 
         try {