Add image version to examples/spark

examples/spark/images/driver/Dockerfile

-FROM gcr.io/google_containers/spark-base
+FROM gcr.io/google_containers/spark-base:1.4.0_v1
 ADD start.sh /start.sh
 CMD ["/start.sh"]

examples/spark/images/master/Dockerfile

-FROM gcr.io/google_containers/spark-base
+FROM gcr.io/google_containers/spark-base:1.4.0_v1
 
 ADD start.sh /
 ADD log4j.properties /opt/spark/conf/log4j.properties

examples/spark/images/worker/Dockerfile

-FROM gcr.io/google_containers/spark-base
+FROM gcr.io/google_containers/spark-base:1.4.0_v1
 
 ADD start.sh /
 ADD log4j.properties /opt/spark/conf/log4j.properties

examples/spark/spark-master.json

@@ -11,7 +11,7 @@
     "containers": [
       {
         "name": "spark-master",
-        "image": "gcr.io/google_containers/spark-master",
+        "image": "gcr.io/google_containers/spark-master:1.4.0_v1",
         "ports": [
           {
             "containerPort": 7077

examples/spark/spark-worker-controller.json

@@ -23,7 +23,7 @@
         "containers": [
           {
             "name": "spark-worker",
-            "image": "gcr.io/google_containers/spark-worker",
+            "image": "gcr.io/google_containers/spark-worker:1.4.0_v1",
             "ports": [
               {
                 "hostPort": 8888,