roles/nginx: Add "ansible managed" string to configs

Generates a placeholder text to say that the file is managed by
ansible.

roles/nginx/templates/blank-vhost.conf.j2

@@ -1,3 +1,5 @@
+# {{ ansible_managed }}
+
 # default blank vhost
 #
 # clients asking for "example.com" should only get a response if we have

roles/nginx/templates/nginx_org_sources.list.j2

@@ -1,3 +1,5 @@
+# {{ ansible_managed }}
+
 {% if ansible_distribution == 'Ubuntu' %}
 {% if nginx_version == "stable" %}
 deb http://nginx.org/packages/ubuntu/ {{ ansible_distribution_release }} nginx

roles/nginx/templates/vhost.conf.j2

@@ -1,3 +1,5 @@
+# {{ ansible_managed }}
+
 {# helper variables and per-site defaults that we can't set in role defaults #}
 {% set domain_name    = item.domain_name %}
 {% set domain_aliases = item.domain_aliases | default("") %}