Expose GIT_COMMIT & BUILD_DATE ARGs as ENV variables (#1159)

http://b/232808996

Author: rosbo

Dockerfile.tmpl

@@ -597,6 +597,9 @@ ARG BUILD_DATE=unknown
 
 LABEL git-commit=$GIT_COMMIT
 LABEL build-date=$BUILD_DATE
+ENV GIT_COMMIT={$GIT_COMMIT}
+ENV BUILD_DATE=${BUILD_DATE}
+
 LABEL tensorflow-version=$TENSORFLOW_VERSION
 # Used in the Jenkins `Docker GPU Build` step to restrict the images being pruned.
 LABEL kaggle-lang=python