CentOS 8+ and Fedora 30+ no longer have the alias "nfs" for "nfs-server"
systemd service.
This shouldn't break backward compatibility, since "nfs-server" service
is available on all supported redhat systems that have systemctl binary.
Fixes#10838
Previously this was very complicated trying to flip between Ruby and
bash. This commit uses a single bash command that decides between yum
and dnf in the script itself.
If guests have the following capabilities, automatic NFS client
installation will be done:
* nfs_client_installed - Checks if the NFS client is installed
* nfs_client_install - Install the NFS client
Support is already in for Debian, Ubuntu, RedHat, CentOS, and Fedora