Now that `ConfigFileFinder.config_file` attribute is used everywhere and
is constructed from the `--config` CLI option, the now unused
`cli_config` parameters can be safely removed.

The `--config` flag is passed into `MergedConfigParser.parse()` and the
module-level function `config.get_local_plugins()`.  Since both of these
places utilize the `ConfigFileFinder` object and the configuration file
override pertains to how configuration behaves, this incremental change
directly associates the `ConfigFileFinder` and the configuration file
override.

The 'ignore_config_files' parameter was accidentally not removed in
c918e72.

Now that `ConfigFileFinder.ignore_config_files` attribute is used
everywhere and is constructed from the `--isolated` CLI option, the now
unused `isolated` parameters can be safely removed.

The `--isolated` flag is passed into `MergedConfigParser.parse()` and
the module-level function `config.get_local_plugins()`.  Since both of
these places utilize the `ConfigFileFinder` object and isolation
pertains to how the `ConfigFileFinder` should behave with respect to
isolation, this incremental change more directly associates the
`ConfigFileFinder` and configuration file isolate.

This fixes a regression introduced in !346 to ensure that `--config` and
`--isolated` are recognized in `aggregate_options()`.

The regression manifested because `aggregate_options()` was relying on
re-parsing `argv` to obtain the option values.  However, !346 changed
the preliminary parsing logic to only parse and "eat" what is necessary
and forward along the options needed before all the configuration was
loaded.  This code path was overlooked because the tests in
`test_aggregator()` were passing but the call from the `Application`
object would never have these options in the remaining `argv` list to be
passed long.

Simplify the initialization code path by invoking
`config.ConfigFileFinder` directly instead of the extra hop by calling
the static class-level `Application.make_config_finder()` method.

Fix --exit-zero when --diff is empty

See merge request pycqa/flake8!391

fixes pycqa/flake8/merge_requests!137