Fix issues with default vs mandatory packages in groups
@mikem this is needed due to how dnf works.
As noted in the following bug, this patch only changes the default for new comps entries. https://bugzilla.redhat.com/show_bug.cgi?id=1303991
Seems sane enough, and doesn't prevent tools from specifying type='default' if they want (though the cli has no option for it currently).
rebased and pushed
Pull-Request has been closed by mikem