Enable SOA serial autoincrement

SOA serial autoincrement is a requirement for major DNS features,
e.g. zone transfers or DNSSEC. Enable it by default in named.conf
both for new and upgraded installations. Name of the bind-dyndb-ldap
option is "serial_autoincrement".

From now on, idnsSOAserial attribute also has to be put to
replication agreement exclude list as serial will be incremented
on each DNS server separately and won't be shared. Exclude list
has to be updated both for new replication agreements and the
current ones.

Minimum number of connections for bind-dyndb-ldap has been rised
to 4 connections, the setting will be updated during package upgrade.

https://fedorahosted.org/freeipa/ticket/2554

install/share/bind.named.conf.template

@@ -46,4 +46,5 @@ dynamic-db "ipa" {
 	arg "sasl_user DNS/$FQDN";
 	arg "zone_refresh $ZONE_REFRESH";
 	arg "psearch $PERSISTENT_SEARCH";
+	arg "serial_autoincrement $SERIAL_AUTOINCREMENT";
 };