Only pull images unless they are available locally

Avoid excessive downloads and only pull images if needed. This makes the
rollout faster and also helps to reduce traffic when cronjobs are used.

lib/cuber/templates/deployment.yml.erb

@@ -100,7 +100,7 @@ spec:
       containers:
       - name: migration
         image: <%= @options[:image] %>:<%= @options[:release] %>
-        imagePullPolicy: Always
+        imagePullPolicy: IfNotPresent
         <%- if @options[:buildpacks] -%>
         command: ["launcher"]
         args: <%= @options[:migrate][:cmd].shellsplit %>
@@ -152,7 +152,7 @@ spec:
       containers:
       - name: <%= procname %>-proc
         image: <%= @options[:image] %>:<%= @options[:release] %>
-        imagePullPolicy: Always
+        imagePullPolicy: IfNotPresent
         <%- if @options[:buildpacks] -%>
         command: ["launcher"]
         args: <%= proc[:cmd].shellsplit %>
@@ -202,7 +202,7 @@ spec:
       initContainers:
       - name: migration-check
         image: <%= @options[:image] %>:<%= @options[:release] %>
-        imagePullPolicy: Always
+        imagePullPolicy: IfNotPresent
         <%- if @options[:buildpacks] -%>
         command: ["launcher"]
         args: <%= @options[:migrate][:check].shellsplit %>
@@ -257,7 +257,7 @@ spec:
           containers:
           - name: task
             image: <%= @options[:image] %>:<%= @options[:release] %>
-            imagePullPolicy: Always
+            imagePullPolicy: IfNotPresent
             <%- if @options[:buildpacks] -%>
             command: ["launcher"]
             args: <%= cron[:cmd].shellsplit %>

lib/cuber/templates/pod.yml.erb

@@ -11,7 +11,7 @@ spec:
   containers:
   - name: pod-proc
     image: <%= @options[:image] %>:<%= @options[:release] %>
-    imagePullPolicy: Always
+    imagePullPolicy: IfNotPresent
     command: ["sleep", "infinity"]
     envFrom:
     - configMapRef: