Adds test-timing keepAlive test

[nicjansma]

PR Checklist:

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
  
• If this is a significant change, an issue has already been created where the problem / solution was discussed: Timings: Tracks 'lookup', adds 'wait' time, fixes connection re-use #2566
  

PR Description

Adds an additional KeepAlive test for #2566, increasing test coverage.

[FredKSchott]

Tests look good, thanks for following up.

Why the two, nested requests? Can you split this into two tests, or add a comment to explain the reason for it?

[nicjansma]

@FredKSchott This new test is specifically testing keep-alive, so we need to have two requests to validate. I've added a comment!

[FredKSchott]

Nice, thanks again! Merging now...