MAGETWO-41440: Update use cases to remove 777 permission to proper permission

 - add constants for default permissions

Author: Dale Sikkema

lib/internal/Magento/Framework/Filesystem/DriverInterface.php

@@ -14,6 +14,16 @@
  */
 interface DriverInterface
 {
+    /**
+     * Permissions to give read/write/execute access to owner and owning group, but not to all users
+     */
+    const WRITEABLE_DIRECTORY_MODE = 0770;
+
+    /**
+     * Permissions to give read/write access to owner and owning group, but not to all users
+     */
+    const WRITEABLE_FILE_MODE = 0660;
+
     /**
      *
      * @param string $path