Unify the case, punctuation and name of test case keywords so they can
be more easily selected or skipped when desired. Add a few keywords that
were missing. Fix a couple of typos in test names.
To make it uniform in all tests, and greppability.
Also:
- replace `-k` flag with `-q` in test 1268. (the actual flag doesn't
matter in this test)
- keep `-k` in test 300 to test its short form.
(also verified to fail without a working `-k`)
Closes#16878
Using this option (only available in debug builds) makes curl always
call curl_easy_duphandle() on the handle before using it.
To help us catch curl_easy_duphandle() mistakes better.
Add a CI job using this.
Bonus: the previous runtests option -e is now also supported as
--test-event
Closes#15504
