hoa://Test/Vfs/ as an alias to atoum\mock\streams\fs\file + atoum://

Can be merge after https://github.com/hoaproject/Test/pull/3.

We use `hoa://Test/Vfs/index.html` as an alias to:
```php
$file = atoum\mock\streams\fs\file::get('index.html');
(string) $file; // will be equal to atoum://…
```

An example is given in https://github.com/hoaproject/Mime/pull/7.
:+1: