Peg base openvino image to 2021.4
Parameterize hard-coded values

Change-Id: I0c3d4866709b5ea98056699818fbac53da979af4
diff --git a/docker/Dockerfile b/docker/Dockerfile
index cf51c5b..0eed995 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,6 +1,5 @@
 #python3 docker_openvino.py build -d cpu -os ubuntu18 --distribution runtime --product_version 2021.4
-#FROM ubuntu18_runtime:2021.4
-FROM openvino/ubuntu18_runtime
+FROM openvino/ubuntu18_runtime:2021.4
 
 USER root