HttpLatencyDetector: cleanup

- Some minor cleanup, following Alex's commits for HttpLatencyDetector
Move code from TestUtils to Asserts, and deprecate

- Deprecate code in TestUtils so we can delete it in 0.6
- Move code to Asserts
- Note: I've been lazy, and not updated uses of it!
  But this is just in test code, and I'll update everything
  first thing in 0.6 work.
AbstractEntity: javadoc for creation order
Merge pull request #631 from aledsage/fix/HttpLatencyDetector-tidies

HttpLatencyDetector: cleanup