Add reverse => reverse option to dns::zone

[ghost]

This will reverse the components of the zone title in addition to
appending .in-addr.arpa to the end.

For example:

dns::zone { '10.23.45':
  ...
  reverse => reverse
  ...
}

would result in a zone definition of:

zone "45.23.10.in-addr.arpa" {
  ...
  file "db.10.23.45"
  ...
}