I've had mdpolicy=group:primary set for all yum-based distros in my
local mock configs for quite a while. I suppose it would be a good
default as AFAIK mock has no use for updateinfo or pkgtags metadata,
and groups metadata is only used during initial chroot setup if the
cmd contains a group, and it's downloaded whenever needed even with
mdpolicy set to group:primary.
Can anyone think of a reason why this wouldn't be a good idea in all
yum-based configs shipped with mock (epel-*.cfg, fedora-22-*.cfg,
fedora-23-*.cfg)? If not, I'll push this soon.