running `rake` loads all files starting with `test_` which is not supposed to also load the helper,
since the helper should be loaded by each test and is not a test itself.
`Puma::Configuration._from_file` was removed in 89f37432de. It was still being used by the `Puma::ControlCLI` class which was previously not being tested while being called with a `--config-file` option.
This PR reintroduces the previous behavior of loading a config file when specified via `pumactl` command.
