Improved the tests for WebSocket polling

[droyad]

This shores up the tests for WebSockets:

• Clarified which certificate was "wrong" by creating a dedicated certificate for that purpose
• Improved assertions to check the message as well -> tests were passing even if certificate was valid due to another error
• Added tests that check for failure on invalid certificates when using WebSocket polling
• Removed inconclusive test assertion in favour of using compiler flag to toggle it in. Makes it clearer when these tests run