plugin/autopath: Add metrics and remove log line (#1143)

* plugin/autopath: Add namespace selector and metrics

Add a namespace, so autopathing only is performed in this namespace.
This will make caching work for the cluster again.

Also export metrics that we've done a successful autopath

* dont shadow

* Fix

* Back the namespacing changes

plugin/autopath/README.md

@@ -24,6 +24,12 @@ Currently the following set of plugin has implemented *autopath*:
 * *kubernetes*
 * *erratic*
 
+## Metrics
+ 
+If monitoring is enabled (via the *prometheus* directive) then the following metric is exported:
+ 
+* `coredns_autopath_success_count_total{}` - counter of successfully autopath-ed queries.
+
 ## Examples
 
 ~~~
@@ -41,5 +47,5 @@ Use the search path dynamically retrieved from the kubernetes plugin.
 
 ## Bugs
 
-When the *cache* plugin is enabled it is possible for pods in different namespaces to get the
-same answer.
+Replies from this plugin are not cached, as the *cache* plugin is configured after this one (see
+plugin.cfg).