Add new test framework files, test for PR #2675

[MSP-Greg]

Description

This PR includes some of the test files for a new test framework that (hopefully) will make it easier to write simpler tests. Also, more complete and reliable tests, more data to see the affects of PR's, etc.

The also adds a test for PR #2675, TestPOpenSSL#test_persistent_close. The test sends twenty requests to a Puma server, after each request, it pauses 1.5 seconds, with config persistent_timeout set to 1 second.

Request time results for master, using Ubuntu 20.04 & Ruby head:

  20 successful requests (10 loops of 2 clients * 1 request per client)
          10%    20%    40%    50%    60%    80%    90%    95%    97%    99%   100% 
    mS      0      0      0    130    330   5740   9540  13020  13020  13020  13520

Request time results for PR #2675, using Ubuntu 20.04 & Ruby head:

  20 successful requests (10 loops of 2 clients * 1 request per client)
          10%    20%    40%    50%    60%    80%    90%    95%    97%    99%   100% 
    mS  2.927  3.049  3.252  3.288  3.320  3.390  3.838  4.876  4.876  4.876  5.707

This shows the benefit of the fixes in PR #2675. Also, there is a new file in the docs folder (test_puma_intro.md), which is the start of a description of the framework, along with comments in the files. Going forward, I may make changes, add benchmark files (some soon), and start to convert the current tests to the new framework. Work in my fork shows they can be much more consistent...

Your checklist for this pull request

• I have reviewed the guidelines for contributing to this repository.
• I have added (or updated) appropriate tests if this PR fixes a bug or adds a feature.
• My pull request is 100 lines added/removed or less so that it can be easily reviewed.
• If this PR doesn't need tests (docs change), I added [ci skip] to the title of the PR.
• If this closes any issues, I have added "Closes #issue" to the PR description or my commit messages.
• I have updated the documentation accordingly.
• All new and existing tests passed, including Rubocop.

[MSP-Greg]

Rebased with PR #2675, all the tests that failed originally should now pass, excepting intermittent failures...

[MSP-Greg]

Will post updated PR soon. I.Hope