Avoid deleting DNS zone when a context is reused
When dnsrecord-del pre_callback detects that the record does
not contain any records, it sets a flag to connection context
and deletes the record object later. However, when more
dnsrecord-del commands share the same context (and this is
the case of "ipa-replica-manage del $MASTER" DNS cleanup), it
may reuse a positive flag from previous dnsrecord-del command
and delete the root DNS zone record and thus effectively delete
the zone.
This patch makes sure that this flag is always initialized to a
sane value in dnsrecord-del pre_callback to make sure that the DNS
zone is not deleted. It also fixes pre_callback function definition
to prevent adding attrs_list to "keys" parameter and thus confuse
developers.
https://fedorahosted.org/freeipa/ticket/2503