Close connections on shutdown

[supersmile2009]

This PR addresses issue #400.
SncRedisBundle::shutdown() function will be called on kernel shutdown in-between unit tests. The same solution is implemented in DoctrineBundle.

I also had to declare snc_redis.session.handler as a public service to be able to fetch it from container in Symfony 4+.

[curry684]

Solution is fine, but I don't think we should be making a service public just for testing purposes. Don't we have some way to do that better?

[supersmile2009]

This is the most elegant and simple solution as to my knowledge.

There is a way to fetch private services from container in tests env, but it's Symfony 4.1 feature: link1, link2

There is a service resetting feature in Symfony 3.4+ symfony/symfony#24155, but it runs on kernel.terminate event, which is not the case with kernel shutdown.
We could reproduce similar feature here by extending a listener from above mentioned Symfony's PR, adding a compiler pass for it, adding some kind of 'kernel.shutdown' event. But it will require people using this bundle to override Symfony\Bundle\FrameworkBundle\Test\KernelTestCase::ensureKernelShutdown() in their tests to dispatch that event in order to benefit from that feature. Too much effort with not a really good result.

The perfect solution would probably be adding existing service resetting feature into kernel shutdown - but that's an issue to be discussed in Symfony repo. And I guess it's going to be Symfony 4.1 feature, I don't think they'll merge it into 4.0.

[dkarlovi]

You can add an env-specific service and prefix it with test..

[curry684]

I'll merge this into 2.1 but keep #400 open so we can fix it better in 3.x.