nameserver: Match A records to reverse[] in named_domains

nameserver: Match A records to reverse[] in named_domains

This will let multiple subnets/domains use the same ipvar

For example, bath and infra-compute can both have a if_25Gb_ip
```
bath14.front.sepia.ceph.com if_25Gb_ip=10.20.192.44
infra-compute-01.os.sepia.ceph.com if_25Gb_1_ip=172.16.53.11

  front.sepia.ceph.com:
    forward: front.sepia.ceph.com
    ipvars:
      - ip
      - if_25Gb_1_ip
    dynamic: true
    ddns_hostname_prefixes:
      - ovh
    reverse:
      - 10.20.192
      - 10.20.193
  os.sepia.ceph.com:
    forward: os.sepia.ceph.com
    ipvar: if_25Gb_1_ip
    dynamic: false
    reverse:
      - 172.16.53
      - 172.16.54

```

`bath14 IN A` will get written to front.sepia.ceph.com
`infra-compute-01 IN A` will get written to os.sepia.ceph.com

Signed-off-by: David Galloway <david.galloway@ibm.com>