Update modules when they have changed

[farridav]

When reading through the nginx module unpacking, and also seeing a commit from @otakup0pe I noticed we are not updating modules when they change (because of the creates arg)

Changing this behaviour so that downloaded nginx modules are used from their extracted location, (which has a version number in it) so if a module version changes, a new one is downloaded, and nginx is recompiled using the newly extracted module (rather than the old one, or a combination of old and new)

[otakup0pe]

This LGTM. We need to keep this style when implementing #4, #2, and whatever else may come.