Ensure Debian substvar generation is deterministic regardless of installed...

class ListDebianSubstvarsAction(argparse._StoreTrueAction):

    def __call__(self, *args, **kwargs):

        # Ensure all comparators are imported so tool_required.all is

        # populated.

        # Attempt to import all comparators so tool_required.all is as

        # populated as possible...

        ComparatorManager().reload()

        tools = tool_required.all

        # ... however for the generated substvar to be effective/deterministic

        # regardless of the currently installed packages we special-case some

        # tools (NB. not package names) as their modules may not have been

        # imported by the `ComparatorManager().reload()` call above. (#908072)

        tools = set((

            'gpg',  # comparators/debian.py

            'rpm2cpio',  # comparators/rpm.py

        ))

        tools.update(tool_required.all)

        packages = set()

        for x in tools:

            try: