Enricher

INT-3465:Content Enricher Improvements
Dead code from here and to the end of this method.
The `ReplyRequiredException` is thrown just from `AbstractReplyProducingMessageHandler`, not from `ContentEnricher`.
1. It is a bad place to test that here. `*ParserTests` are just for parsers, not the logic of target component. Yes, we have many places with logic, but now we try to follow with that rule.
2. `@Test(expected=)` is bad by nature. As you see with wrong test-case we are getting dead code.
We'd prefer to do something like this: `LoggingChannelAdapterParserTests#failConfigLogFullMessageAndExpression`
`try...catch` for the expected block.
3. I didn't say to write similar test. You just should run all test from debug and check the break point on the `return null;` from `ContentEnricher.handleRequestMessage`. If it won't break there, we don't have the test for  enricher's `null`. Then you should produce it. Here `ContentEnricherTests`.
4. The `null` result you can achieve only with `replyTimeout` for the enricher's sub-flow gateway. The underlying messageHandler just should `Thread.sleep()`, more than enricher's wait timeout.

Am I clear?