F30: dnf, yum, mock

[John Pilkington]

Fedora 30 had several dnf-related updates today.  Since then, mock fails 
with KeyError: 'yum.conf'

In the mockbuild directory, /var/lib/mock/Fedora.../root/etc/yum.conf is 
a link to yum/yum.conf, which is a 0 byte file.

In the corresponding file for epel-7 builds, last used before the 
updates, yum/yum.conf is 3.2 kB

In the F30 host /etc/yum.conf is now 816 bytes

Perhaps I should try to revert.

John P