Bug 1526147 - Update oc run instructions to include cluster name

Author: dymurray

apb_devel/writing/reference.adoc

@@ -726,7 +726,7 @@ $ oc run <pod_name> \
       --restart=Never \
       --attach=true \
       --serviceaccount=apb \
-      -- <action> -e namespace=<target_namespace> -e cluster=$CLUSTER
+      -- <action> -e namespace=<target_namespace> -e cluster=openshift
 ----
 <1> Use the pull specification for the image shown when running `oc get images` from
 the previous step, since the registry will determine the fully-qualified domain