Code review comment for ~d-info-e/cloud-init:fix-user-group-doc

hi scott,
i have addressed your point 2), but not yet 1) as i am still unsure if it will break something or not. looking at it a bit more closer i believe any '-' in the cc_user_group module should be replaced if it really works both ways. that also would include others like primary-group, selinux-user, ect. see cloud-config-user-groups.txt for more. what do you think about that?