varnish: add "name" parameter

recipes/varnish.rb

@@ -1,16 +1,23 @@
 include_recipe "datadog::dd-agent"
 
 # Monitor Varnish
-# 
-# Assuming you have 2 clusters, one tagged and one with a custom
-# path to varnishstat
-# you need to set up the following attributes
+#
+# You'll need to set up the following attributes:
 # node.datadog.varnish.instances = [
+#
+#   # Path to varnishstat (required)
 #   {
 #     :varnishstat => "/opt/local/bin/varnishstat"
 #   },
+#
+#   # Tags to apply to all varnish metrics (optional)
 #   {
 #     :tags => ["test", "cache"]
+#   },
+#
+#   # Varnish instance name, passed to varnishstat -n (optional)
+#   {
+#     :name => "myvarnish0"
 #   }
 # ]
 

templates/default/varnish.yaml.erb

@@ -1,6 +1,9 @@
 instances:
 <% @instances.each do |i| -%>
   - varnishstat: <%= i["varnishstat"] || "/usr/bin/varnishstat" %>
+  <% if i.key?("name") -%>
+    name: <%= i["name"] %>
+  <% end -%>
   <% if i.key?("tags") -%>
     tags:
     <% i["tags"].each do |t| -%>