Support custom config for InfluxDB

The InfluxDB config file is an exotic format containing nested
sections, for example  ```[[foo]]```, and doesn't work with
merge_configs. To support customising the config this patch adds
support for overriding at the file level.

Change-Id: I05b18c43c3a18e9b46dc450565bc1e156b4ff9dd
Closes-Bug: #1757186
Partially-Implements: blueprint monasca-roles

ansible/roles/influxdb/tasks/config.yml

@@ -30,7 +30,7 @@
   vars:
     service: "{{ influxdb_services['influxdb']}}"
   template:
-    src: "{{ role_path }}/templates/{{ item }}.conf.j2"
+    src: "{{ item }}"
     dest: "{{ node_config_directory }}/influxdb/influxdb.conf"
     mode: "0660"
   become: true
@@ -38,8 +38,10 @@
   when:
     - inventory_hostname in groups[service.group]
     - service.enabled | bool
-  with_items:
-    - "influxdb"
+  with_first_found:
+    - "{{ node_custom_config }}/influxdb/{{ inventory_hostname }}/influxdb.conf"
+    - "{{ node_custom_config }}/influxdb.conf"
+    - "influxdb.conf.j2"
   notify:
     - Restart influxdb container