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.
Now that the `ConfigFileFinder` has the `.ignore_config_files`
attribute, switch the relevant code paths to utilize this public
attribute.
Tests have been updated to either construct `ConfigFileFinder` or mock
the object appropriately.
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.
We introduce a new `ArgumentParser` for registering the preliminary
options to be inherited by the `Application.option_manager`. The next
step will be to use the `Application.prelim_arg_parser` for parsing and
handling preliminary options and arguments.
Note that we prevent the preliminary parser from handling `-h/--help`
and defer to that to the primary parser.
Now that `args` parameters is not being used, it is safe to remove from
the constructor signature.
Further work is required to evaluate and clean-up tearing out the
threading-through of `args` from various callers and tests.
This relies on two things:
1. Properly configuring flake8-import-order to use that style
2. Properly configuring flake8-import-order to know that flake8 is our
application name.
