dns: Add support for NOT managing resolv.conf

This is important for systems using Puppet and DHCP, because DHCP renewals
rewrite resolv.conf, which then gets re-re-written by Puppet.

NEWS

 unreleased (??)
 
+    [dns] Add support for disabling Puppet management of resolv.conf, for 
+    systems using DHCP (akkornel)
+
     [remctl] Require remctl-server package be installed before installing 
     xinetd config (akkornel)
 

manifests/dns.pp

 # Defines the DNS configuration of a system.
 
-class base::dns {
-  base::dns::resolv_conf { $::fqdn_lc: ensure => present }
+# You may set $no_resolv_conf to prevent Puppet from overriding the system's
+# resolv.conf file.  This is helpful in DHCP environments.
+# To enable, use Hiera to set base::dns::no_resolv_conf to "true".
+class base::dns(
+  $no_resolv_conf = false
+) {
+  if !$no_resolv_conf {
+    base::dns::resolv_conf { $::fqdn_lc: ensure => present }
+  }
 }