Harden ITs of content feed

I discovered that the content-feed ITs (all tests extending com.onehippo.cms7.contentfeed.test.AbstractPlatformWithHstServicesIT) have some issues with cleaning up, which results to errors if any class has multiple test methods (more than 1).

Plus, the ContentFeedDaemonModule initialises itself automatically, but it does not destroy itself. Making it a blocker when attempting to run multiple test methods. Fyi, all our ITs shutdown and re-initialise component manager and services (eg PlatformAvailableService - on which the ContentFeedDaemonModule triggers) for every test method.

Plus, small improvements, see commit message.