Related to https://build.spring.io/browse/INT-MASTERSPRING40-JOB1-1271
* Fix race condition with subscription in the `FluxMessageChannel`:
rely on the `doOnRequest()` to start producing from upstream publishers
* Remove `SourcePollingChannelAdapterTests` since
`Class.getDeclaredConstructor().newInstance()` doesn't rethrow an exception as is
but wrap it into the `InvocationTargetException`.
This is probably the main reason to deprecate a regular `Class.newInstance()`
* Use `LettuceConnectionFactory.setEagerInitialization(true)` in the `RedisAvailableRule`
to avoid possible dead lock with lazy init
* Adjust Redis tests for new `RedisAvailableRule` behavior
efcc01804c