Directories under /etc/yum/* need to make way for ../dnf symlinks after upgrade.

[pirat89]

original report by @cwyamz

preforming an upgrade from 7.6 to 8 using leapp the user is required to dnf install yum due to yum being in the to_remove file but the transaction fails:
Error unpacking rpm package yum-4.0.9-1.el8.noarch
"error: unpacking of archive failed on file /etc/yum/pluginconf.d: cpio: File from package already exists as a directory in system"

The work around is to rename /etc/yum to /etc/yum.bak and retry.
More info here: https://bugzilla.redhat.com/show_bug.cgi?id=1626736#c9

libdnf-0.22.3-1.el8.x86_64
dnf-4.0.9-1.el8.noarch
leapp-0.4.0-1.el7_5.noarch

EDIT: See #29 for additional info.

[vojtechsokol]

To preserve contents of the /etc/yum folder you can also try this:

# check contents of the folders
ls -l /etc/dnf/**
ls -l /etc/yum/**

# move to new destination
mv /etc/yum/pluginconf.d/* /etc/dnf/plugins/
mv /etc/yum/protected.d/* /etc/dnf/protected.d/
mv /etc/yum/vars/* /etc/dnf/vars/

# cleanup
rmdir /etc/yum/pluginconf.d/ /etc/yum/protected.d/ /etc/yum/vars/

# relink
ln -s ../dnf/plugins/ /etc/yum/pluginconf.d
ln -s ../dnf/protected.d/ /etc/yum/protected.d
ln -s ../dnf/vars/ /etc/yum/vars

# check again
ls -l /etc/dnf/**
ls -l /etc/yum/**