Improve configuration change detection (#2656)

* Use information about the configuration configmap to determine changes

* Add hashstructure dependency

* Rename queue functions

* Add test for configmap checksum

rootfs/etc/nginx/template/nginx.tmpl

@@ -7,6 +7,8 @@
 {{ $proxyHeaders := .ProxySetHeaders }}
 {{ $addHeaders := .AddHeaders }}
 
+# Configuration checksum: {{ $all.Cfg.Checksum }}
+
 # setup custom paths that do not require root access
 pid /tmp/nginx.pid;