e2e: examples: fix test image reference

Author: sjenning

test/fixtures/doc-yaml/user-guide/secrets/secret-pod.yaml.in

@@ -5,8 +5,8 @@ metadata:
 spec:
   containers:
     - name: test-container
-      image: {{.MounttestImage}}
-      command: [ "/mounttest", "--file_content=/etc/secret-volume/data-1" ]
+      image: {{.AgnhostImage}}
+      args: [ "mounttest", "--file_content=/etc/secret-volume/data-1" ]
       volumeMounts:
           # name must match the volume name below
           - name: secret-volume