Use the new vault.centos.org repos. Fix the yum repo configs in the
image if necessary to use these new repos.
Use the standard centos images from the centos registry rather than
custom lsr images from dockerhub.
Add support for centos8. Note that using ansible 2.7 on centos8
requires setting /usr/bin/python3 to be the ansible python
interpreter. Later versions of ansible have better auto-detection.
We can get rid of this once we drop support for ansible 2.7
Use tox-lsr 1.0.1 - which means we do not need
molecule_extra_requirements.txt
Signed-off-by: Rich Megginson <rmeggins@redhat.com>
