collectd: Add DaemonSet for collectd

Since all the nodes in the cluster run Fedora CoreOS now, we can
deploy collectd as a container, managed by a DaemonSet.

Note that while _collectd_ has to run as _root_ in order to collect
a lot of metrics, it should not run with all privileges.  It does need
to run as a "super-privileged container" (`spc_t` SELinux domain), but
it does _not_ need most kernel capabilities.

collectd/collectd.yaml

@@ -0,0 +1,74 @@
+---
+apiVersion: apps/v1
+kind: DaemonSet
+metadata:
+  name: collectd
+  labels:
+    app.kubernetes.io/name: collectd
+    app.kubernetes.io/component: collectd
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: collectd
+      app.kubernetes.io/component: collectd
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: collectd
+        app.kubernetes.io/component: collectd
+    spec:
+      containers:
+      - name: collectd
+        image: git.pyrocufflink.net/containerimages/collectd
+        ports:
+        - containerPort: 9103
+          name: http
+        readinessProbe: &probe
+          httpGet:
+            port: http
+            path: /metrics
+          periodSeconds: 60
+        startupProbe:
+          <<: *probe
+          periodSeconds: 1
+          successThreshold: 1
+          failureThreshold: 30
+          timeoutSeconds: 1
+        securityContext:
+          capabilities:
+            add:
+            - DAC_READ_SEARCH
+            drop:
+            - ALL
+          seLinuxOptions:
+            type: spc_t
+          readOnlyRootFilesystem: true
+        volumeMounts:
+        - mountPath: /etc/collectd.d
+          name: config
+          readOnly: true
+        - mountPath: /host
+          name: host
+        - mountPath: /run
+          name: host
+          subPath: run
+        - mountPath: /tmp
+          name: tmp
+      hostNetwork: true
+      hostPID: true
+      hostIPC: true
+      tolerations:
+      - effect: NoExecute
+        operator: Exists
+      - effect: NoSchedule
+        operator: Exists
+      volumes:
+      - name: config
+        configMap:
+          name: collectd
+      - name: host
+        hostPath:
+          path: /
+      - name: tmp
+        emptyDir:
+          medium: Memory