dlz: Add dlz cloud and cloud_reverse drivers

Compilation:
------------
./configure --with-dlz-cloud --with-dlz-cloud-reverse
make
make install

Configuration directive needed:
-------------------------------

You must run bind9 with the "empty-zones-enable no;" options in the proper place.

dlz_cloud:
----------

The dlz_cloud driver can be used to declare a dynamically generated zone looking
like the AWS private ips zones.

The syntax to declare such a zone is:

dlz "zone_name" {
    database "dlz_cloud zone_name dns_server";
};

dlz_cloud is the name of the plugin.

The dns_server is served in the SOA records.

ip-192-168-4-5.zone_name willl be resolved into 192.168.4.5.

The name to resolve must start with ip- else the resolution will fail.

Sample declaration:

dlz "eu-west-1.compute.internal" {
    database "dlz_cloud eu-west-1.compute.internal dew.nodalink.com.";
};

dlz_cloud_reverse:
------------------

The dlz_cloud_reverse driver is used to implement a dynamically generated reverse
zone looking like the AWS private ips reverse zone.

The syntax to declare such a zone is:

dlz "zone_name" {
    database "dlz_cloud_reverse zone_name dns_server reverse_suffix";
}

dlz_cloud_reverse is the name of the plugin

The dns_server is served in the SOA records.

reverse_suffix is appended at the end of the resolved name.

10.1.1.2 will we resolved back in ip-10-1-1-2.eu-west-1.compute.internal

Note that all resolved back name starts with ip-.

dlz "10.in-addr.arpa" {
   database "dlz_cloud_reverse 10.in-addr.arpa dew.nodalink.com. .eu-west-1.compute.internal";
};