The #1611 patch does not treat the user provider as a service

[skalpa]

@henrikbjorn @hkdobrev To create an alias to an already registered service you have to use a closure that accesses the service and cannot just copy the factory with raw(). Failure to do so may result in the instanciation of your object twice.

In the new test, this will fail while it should work:
$this->assertSame($app['my_user_provider'], $app['security.user_provider.default']);

To fix that, you need to replace $users = $app->raw($users) in the provider with:

$users = function () use ($app, $users) {
    return $app[$users];
};

PS: Apologies for not sending a PR, I'm barely able to find free time for reviews.

[hkdobrev]

Thanks! Addressed in #1631.