Install yum on CentOS8/Fedora
Install yum on CentOS8/Fedora

Currently beaker-puppet requires yum command while installing required
packages, and it fails on CentOS8/Fedora which doesn't have yum by
default.
This patch makes sure that yum is installed while preparing a test node
so that we can avoid the error caused by missing yum.

Change-Id: I780d2d221f0209e914514398c61c7a45fa33ffcf

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration