Consistent on my macBook and also affecting Travis-CI runs.

I believe @JamesWTruher was investigating if there is a race condition between the test listener being ready and the test case not receiving a response.

Replace HttpListener tests:

• response (Replace HttpListener Response Tests with WebListener #5540)
• echo (Replace HttpListener Echo Tests with WebListener #5840)
• redirect (Replace HttpListener Redirect Tests with WebListener #5872)
• linkheader (Replace HttpListener Link Header Tests with WebListener #5806)
• Disabled HttpListener from starting