bpo-33718: regrtest: use "xxx then yyy" result if re-run (GH-7521) (GH-7562)

If tests are re-run, use "xxx then yyy" result format (ex: "FAILURE
then SUCCESS") to show that some failing tests have been re-run.

Add also test_regrtest.test_rerun_fail() test.

(cherry picked from commit c45fc7673e23f911639d10d3771ffef7be870c7a)
2 files changed