Use explicit concat ordering for zonefile contents

Previously relied on the resource name to achieve ordering of zone file
concat fragments. The zone file header fragment is given the resource name
"00.bind.${name}" and the record entry fragements get the resource name
"${zone}.${record_type}.${name}". This works fine until you use a reverse
zone that starts with a 0. In that case the implicit filename ordering gets
reversed as the record fragments end up looking like
"0_168_192.in-addr.arpa.PTR.PTR hostname" which by name ordering end up
coming before the header that starts with "00".