Use DNS forwarders in /etc/named.conf

This patch adds options --forwarder and --no-forwarders. At least one of
them must be used if you are doing a setup with DNS server. They are
also mutually exclusive. The --forwarder option can be used more than
once to specify more servers. If the installer runs in interactive mode,
it will prompt the user if none of these option was given at the command
line.

ipaserver/install/bindinstance.py

@@ -52,6 +52,7 @@ class BindInstance(service.Service):
         self.host = None
         self.ip_address = None
         self.realm = None
+        self.forwarders = None
         self.sub_dict = None
 
         if fstore:
@@ -59,12 +60,13 @@ class BindInstance(service.Service):
         else:
             self.fstore = sysrestore.FileStore('/var/lib/ipa/sysrestore')
 
-    def setup(self, fqdn, ip_address, realm_name, domain_name, named_user="named"):
+    def setup(self, fqdn, ip_address, realm_name, domain_name, forwarders, named_user="named"):
         self.named_user = named_user
         self.fqdn = fqdn
         self.ip_address = ip_address
         self.realm = realm_name
         self.domain = domain_name
+        self.forwarders = forwarders
         self.host = fqdn.split(".")[0]
         self.suffix = util.realm_to_suffix(self.realm)
 
@@ -146,11 +148,20 @@ class BindInstance(service.Service):
         self.chkconfig_on()
 
     def __setup_sub_dict(self):
+        if self.forwarders:
+            fwds = "\n"
+            for forwarder in self.forwarders:
+                fwds += "\t\t%s;\n" % forwarder
+            fwds += "\t"
+        else:
+            fwds = " "
+
         self.sub_dict = dict(FQDN=self.fqdn,
                              IP=self.ip_address,
                              DOMAIN=self.domain,
                              HOST=self.host,
                              REALM=self.realm,
+                             FORWARDERS=fwds,
                              SUFFIX=self.suffix,
                              REVERSE_HOST=self.reverse_host,
                              REVERSE_SUBNET=self.reverse_subnet)