add support for ldap plugin in rhel6
add support for ldap plugin in rhel6

luxflux/puppet-openvpn,to-kn/puppet-openvpn,jkroepke/puppet-openvpn,luxflux/puppet-openvpn,luxflux/puppet-openvpn,jkroepke/puppet-openvpn,jkroepke/puppet-openvpn,to-kn/puppet-openvpn,to-kn/puppet-openvpn