Revert to md2man master

Upstream md2man is working again.  We can revert to using it instead
of a specific commit id.

Also, add make integration.CentOS for testing

Signed-off-by: baude <bbaude@redhat.com>

Closes: #320
Approved by: rhatdan

.papr_prepare.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -xeuo pipefail
 
-DIST=$(cat /etc/redhat-release  | awk '{print $1}')
+DIST=${DIST:=Fedora}
 IMAGE=fedorapodmanbuild
 PYTHON=python3
 if [[ ${DIST} != "Fedora" ]]; then