Add helm test

Usage: helm test <release-name> --cleanup

charts/virtual-kubelet/templates/tests/helloworld.yaml

@@ -0,0 +1,26 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: "{{ .Release.Name }}-{{ .Release.Revision }}-test"
+  labels:
+    role: test
+  annotations:
+    "helm.sh/hook": test-success
+spec:
+  containers:
+  - image: hello-world:linux
+    imagePullPolicy: Always
+    name: helloworld
+    resources:
+      requests:
+        memory: "0.1G"
+        cpu: 10m
+      limits:
+        memory: "0.1G"
+        cpu: 10m
+  dnsPolicy: ClusterFirst
+  nodeName: "{{ .Values.nodeName }}"
+  restartPolicy: Never
+  tolerations:
+  - key: "{{ .Values.nodeTaint }}"
+    effect: NoSchedule