guest/redhat: fix nfs client installation
guest/redhat: fix nfs client installation

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

sni/vagrant,marxarelli/vagrant,mitchellh/vagrant,sni/vagrant,chrisroberts/vagrant,gitebra/vagrant,sni/vagrant,sni/vagrant,mitchellh/vagrant,chrisroberts/vagrant,gitebra/vagrant,mitchellh/vagrant,marxarelli/vagrant,marxarelli/vagrant,chrisroberts/vagrant,marxarelli/vagrant,gitebra/vagrant,mitchellh/vagrant,chrisroberts/vagrant,gitebra/vagrant