Allow multiple places to install curl

Curl is an important package that we end up needing in a few places. To
avoid puppet unique name conflicts with the package "curl" only define
the curl package resource if it isn't already defined.

This allows us to define it in multiple places that may or may not
overlap depending on how hosts are constructed.

Change-Id: I8b346cbfb908c5d2094c5e46ff008ef735b0e903

manifests/init.pp

@@ -49,8 +49,10 @@ class etherpad_lite (
     ensure => present,
   }
 
-  package { 'curl':
-    ensure => present,
+  if !defined(Package['curl']) {
+    package { 'curl':
+      ensure => present,
+    }
   }
 
   anchor { 'nodejs-package-install': }