Add support for NFSv4 clients on RHEL variants.

I also have the following in a profile to set idmapd domain (using puppetlabs-inifile module):

class profiles::nfs {
  ini_setting { 'idmapd_domain':
    ensure  => present,
    path    => '/etc/idmapd.conf',
    section => 'General',
    setting => 'Domain',
    value   => $::domain,
    notify  => Service['rpcidmapd']
  }
}