You can now exclude arches in koji_directive or koji_utils. This is
useful for task-abicheck, which doesn't need to download noarch RPMs.
This also modified arch_utils to include a mapping from base arches to
binary arches, and improved behavior in koji_utils when the user
requests only base arches to be downloaded - we now correctly convert it
to concrete binary arches, because that's what Koji requires as input.
As a minor point, typo in armv7hl has been fixed.
I guess the self. for these variables (plus self.target_dir) is for testing purposes, as it really does not make much sense otherwise. Or is there any other reason?