add drift and fixing group request response time to include also sending part
- also small refactoring and update in test
organize imports
Merge pull request #1852 from pwielgolaski/jms_group

JMS: Add drift and fixing group request response time to include also sending part
* Added basic support for end-to-end integration tests using WireMock, as well as a test for issue #1845
* HttpEngine now shuts down thread pool on termination.
* Made Netty thread pool accessible (and possible to shut down) in HttpEngine.
* Added awaitTermination to ActorSupport - in some cases, we have a race condition where shutdown code wasn't being called before services were restarted.