Keep only the generated files needed for tests. Place generated
intermediaries in `tests/certs/gen` where they are ignored by git. No
longer generated `*.dhp` files.
Have a shorter naming scheme: `test-ca` instead of `EdelCurlRoot-ca` and
`test-localhost` instead of `Server-localhost-sv`, etc.
Remove the `stunnel` certificate as it was nearly a duplicate of
`test-localhost`.
No longer copy a generated certificates to `tests/stunnel.pem`. Let test
server default to `certs/test-localhost.pem` instead.
Closes#16593
