[feature/avatars] Differentiate tests for get drivers functions

Tests for get_all_drivers() and get_enabled_drivers() should be different.

PHPBB3-10018

tests/avatar/driver/barfoo.php

@@ -0,0 +1,19 @@
+<?php
+
+class phpbb_avatar_driver_barfoo extends phpbb_avatar_driver
+{
+	public function get_data($row)
+	{
+		return array();
+	}
+
+	public function prepare_form($request, $template, $row, &$error)
+	{
+		return false;
+	}
+
+	public function process_form($request, $template, $row, &$error)
+	{
+		return false;
+	}
+}