stick oc to version 4.15

Author: bmeng

Dockerfile

@@ -43,7 +43,7 @@ ARG GITHUB_URL="https://api.github.com"
 ARG GITHUB_TOKEN=""
 
 # Replace version with a version number to pin a specific version (eg: "4.7.8")
-ARG OC_VERSION="stable"
+ARG OC_VERSION="stable-4.15"
 ENV OC_URL="https://mirror.openshift.com/pub/openshift-v4/x86_64/clients/ocp/${OC_VERSION}"
 
 # Replace "/latest" with "/tags/{tag}" to pin to a specific version (eg: "/tags/v0.4.0")