Describe bug scenario when failing step disables AfterStep hook

Covers #504
Fixes the bug scenario where failing test disables AfterStep hook

Fixes #504
Refactor & cleanup RuntimeScenarioTester and StepContainerTester
Fix the discrepency in the way background setup is handled
Merge pull request #505 from Behat/bugfix/step-hooks-with-failed-step

Step hooks with failed step