test: avoid panics in registry tests helper

What does this MR do?

I notice from time to time that some tests are failing with a very long log output and no apparent errors/failed assertions. I have strong suspicion that the failure is happening in the shutdown function because we panic in the tests, or at least it masks underlying problem.

In order to test this idea, I have adjusted the shutdown function to return error from now plus used t.Cleanup instead of defer which should add much more meaningful assertion failures. The shutdown function now also tries to shutdown all components even if error occurs, instead of stopping(panicing) on the first error). Additionally I discovered that in some of the tests the env environment was reassigned with a new one (e.g. after pre-seeding of the repo) which was causing the old env to not to be properly shutdown as the final defer was called using the last value of env reference.

In theory, we should be shutting down the first env before we create another, but this would require much more refactoring (i.e. splitting server shutdown from DB and Redis shutdown). This MR does not makes things worse in this regard. Let's gather more data (e.g. more detailed assertion failures) before we decide to clean-up/refactor this as well.

Related to #1562 (closed)

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