s4-rpc: dnsserver: return DNS_RANK_NS_GLUE recors when explicitly asked for

s4-rpc: dnsserver: return DNS_RANK_NS_GLUE recors when explicitly asked for

NS records should be included in the query for sub-domains.  NS records
got dropped when the rank for NS records was correctly set to NS_GLUE
from ZONE in commit 2036cbd9249c84d9b46370f0e8cd6a0264c737ba.

  samba-tool dns query 172.31.9.161 s4xdom.base @ ALL
  =>
  Name=glue, Records=0, Children=0

  samba-tool dns query 172.31.9.161 s4xdom.base glue ALL
  =>
    Name=, Records=1, Children=0
      NS: glue.dns.private. (flags=40000082, serial=21, ttl=900)

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10751

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Thu Sep  4 14:37:51 CEST 2014 on sn-devel-104

(cherry picked from commit 0b4a3b76111411e8969932a3da4ffab989e0da4c)