python/remove_dc: handle dnsNode objects without dnsRecord attribute

python/remove_dc: handle dnsNode objects without dnsRecord attribute

If we have dnsNode objects without dnsRecord attribute values we trigger
the following error triggered by 'samba-tool domain demote --remove-other-dead-server=server2'

  ERROR(<type 'exceptions.TypeError'>): uncaught exception - __ndr_unpack__()
  argument 1 must be string or read-only buffer, not dnsp.DnssrvRpcRecord
    File "/usr/lib64/python2.6/site-packages/samba/netcmd/__init__.py", line 175,
  in _run
      return self.run(*args, **kwargs)
    File "/usr/lib64/python2.6/site-packages/samba/netcmd/domain.py", line 720, in
  run
      remove_dc.remove_dc(samdb, logger, remove_other_dead_server)
    File "/usr/lib64/python2.6/site-packages/samba/remove_dc.py", line 423, in
  remove_dc
      remove_dns_account=True)
    File "/usr/lib64/python2.6/site-packages/samba/remove_dc.py", line 351, in
  offline_remove_ntds_dc
      remove_dns_account=remove_dns_account)
    File "/usr/lib64/python2.6/site-packages/samba/remove_dc.py", line 266, in
  offline_remove_server
      remove_dns_references(samdb, logger, dnsHostName)
    File "/usr/lib64/python2.6/site-packages/samba/remove_dc.py", line 186, in
  remove_dns_references
      for v in values if not to_remove(v) ]
    File "/usr/lib64/python2.6/site-packages/samba/remove_dc.py", line 160, in
  to_remove
      dnsRecord = ndr_unpack(dnsp.DnssrvRpcRecord, value)
    File "/usr/lib64/python2.6/site-packages/samba/ndr.py", line 45, in ndr_unpack
      object.__ndr_unpack__(data, allow_remaining=allow_remaining)
  A transaction is still active in ldb context [0xe1f320] on
  tdb:///var/lib/samba/private/sam.ldb

"next" is used in perl not in python!

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12018

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed Jul 13 10:10:30 CEST 2016 on sn-devel-144

(cherry picked from commit f8181360a89ac9e53cc991e966958e496271fa15)