Fixing coding style, add tests/config.user.php for custom test databases

[jakobsack]

Adds the usual style fixes.

I additionally added an option to use a custom database for testing. With the changes you can create the file tests/config.user.php with some content like

<?php
$userConfig = [
    'SABRE_MYSQLDSN'  => 'mysql:host=127.0.0.1;dbname=sabredav_test',
    'SABRE_MYSQLUSER' => 'sabredav',
    'SABRE_MYSQLPASS' => 'sabredav',
];

to set the test database without adding the environment variables.