HTK: Update k8s-entrypoint container macro to add security context

This PS updates the htk k8s-entrypoint container macro to add security
context, with a set of defaults to allow operation with existing charts.

Change-Id: Ib41600e2e3c848ae0d62181ad7e01f3cf00a26a0
Signed-off-by: Pete Birley <pete@port.direct>

helm-toolkit/templates/snippets/_kubernetes_entrypoint_init_container.tpl

@@ -50,12 +50,34 @@ values: |
     etcd:
       hosts:
         default: etcd
+  # NOTE (portdirect): if the stanza, or a portion of it, under `pod` is not
+  # specififed then the following will be used as defaults:
+  #  pod:
+  #    security_context:
+  #      kubernetes_entrypoint:
+  #        container:
+  #          kubernetes_entrypoint:
+  #            runAsUser: 65534
+  #            readOnlyRootFilesystem: true
+  #            allowPrivilegeEscalation: false
+  pod:
+    security_context:
+      kubernetes_entrypoint:
+        container:
+          kubernetes_entrypoint:
+            runAsUser: 0
+            readOnlyRootFilesystem: false
 usage: |
   {{ tuple . "calico_node" list | include "helm-toolkit.snippets.kubernetes_entrypoint_init_container" }}
 return: |
   - name: init
     image: "quay.io/stackanetes/kubernetes-entrypoint:v0.3.1"
     imagePullPolicy: IfNotPresent
+    securityContext:
+      allowPrivilegeEscalation: false
+      readOnlyRootFilesystem: false
+      runAsUser: 0
+
     env:
       - name: POD_NAME
         valueFrom:
@@ -89,6 +111,18 @@ return: |
       []
 */}}
 
+{{- define "helm-toolkit.snippets.kubernetes_entrypoint_init_container._default_security_context" -}}
+Values:
+  pod:
+    security_context:
+      kubernetes_entrypoint:
+        container:
+          kubernetes_entrypoint:
+            runAsUser: 65534
+            readOnlyRootFilesystem: true
+            allowPrivilegeEscalation: false
+{{- end -}}
+
 {{- define "helm-toolkit.snippets.kubernetes_entrypoint_init_container" -}}
 {{- $envAll := index . 0 -}}
 {{- $component := index . 1 -}}
@@ -110,9 +144,11 @@ return: |
 {{- end -}}
 {{- end -}}
 {{- $deps := $envAll.Values.__kubernetes_entrypoint_init_container.deps }}
-
+{{- $default_security_context := include "helm-toolkit.snippets.kubernetes_entrypoint_init_container._default_security_context" . | fromYaml }}
+{{- $patchedEnvAll := mergeOverwrite $default_security_context $envAll }}
 - name: init
 {{ tuple $envAll "dep_check" | include "helm-toolkit.snippets.image" | indent 2 }}
+{{- dict "envAll" $patchedEnvAll "application" "kubernetes_entrypoint" "container" "kubernetes_entrypoint" | include "helm-toolkit.snippets.kubernetes_container_security_context" | indent 2 }}
   env:
     - name: POD_NAME
       valueFrom: