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
(cherry picked from commit 5ee64a6881)