Force to use markdown to prevent pypi issue
Force to use markdown to prevent pypi issue

Recently the pypi team have reintroduce some deactivated tests
on package deployment and especially tests concerning long_description
syntaxe.

If projects don't specify that they use the markdown format the
package deployment will fail if something went wrong in the markdown format.

By example if a project use inline literal this can be an issue due to
the fact that if `long_description_content_type` is missing [1]. The
default format will be `text/x-rst` where code block is different from
markdown.

These changes force to use the markdown format to avoid this kind of issue
on project who use `README` at markdown format.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2019-July/007459.html

For more details:
https://github.com/pypa/warehouse/issues/5890#issuecomment-494868157

Change-Id: If1be877b265f36078a5e66a13b7ab55db699af0f

openstack/puppet-tripleo,openstack/puppet-tripleo,openstack/puppet-tripleo