Fix tests in AfterPipelineFixture.  When adding piplines, instead of asserting on the items added, assert using the collection items.
BeforePipeline test fixes
Fixes HandleRequest_prereq_returns_response_should_still_run_postreq (ensure running post-hooks even if pre-hook returns a response)
Several NancyEngineFixture test fixes where instead of throwing an exception in the mocks, a faulted task is returned.
Use InnerException from the task's aggregate exception when InvokingOnErrorHook