handle docker host in prometheus config

templates/conf/prometheus.yml.j2

@@ -338,3 +338,20 @@ scrape_configs:
         regex: '(.*):9150'
         replacement: '${1}'
 {% endif %}
+
+{% if prometheus_docker_exporter_targets is defined %}
+  # Docker exporter #
+  - job_name: docker
+    scrape_interval: 30s
+    scrape_timeout: 10s
+    static_configs:
+      - targets:
+{% for target in prometheus_memcached_exporter_targets %}
+        - {{ target }}:9323
+{% endfor %}
+    relabel_configs:
+      - source_labels: [ __address__ ]
+        target_label: instance
+        regex: '(.*):9323'
+        replacement: '${1}'
+{% endif %}