MAGETWO-43265: An exception if try to get to the Web Wizard without writable file permissions

- added model wrapper over file_exists
- fixed unit-tests

Author: Ivan Gavryshko

setup/src/Magento/Setup/Model/ApplicationStatus.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Copyright © 2015 Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Setup\Model;
+
+/**
+ * Class ApplicationStatus
+ * Returns status of application
+ */
+class ApplicationStatus
+{
+    /**
+     * Path to Magento config
+     */
+    const PATH_TO_CONFIG = '/app/etc/config.php';
+
+    /**
+     * Returns status of application
+     *
+     * @return bool
+     */
+    public function isApplicationInstalled()
+    {
+        return file_exists(BP . self::PATH_TO_CONFIG);
+    }
+}