r/collectd: Manage collectd.d directory

The `/etc/collectd.d` directory is created by the RPM package on
machines running a Red Hat-based Linux distribution, but it may not
always be present on other machines.

roles/collectd/tasks/main.yml

@@ -23,6 +23,14 @@
   tags:
   - collectd-config
 
+- name: ensure collectd config drop-in directory exists
+  file:
+    path: /etc/collectd.d
+    mode: u=rwx,go=rx
+    state: directory
+  tags:
+  - collectd-config
+
 - name: ensure collectd directory exists
   file:
     path: /etc/collectd