Core part improvements.

* node group tmpl props are now copied to the node group
* imaage_id is now taken from cluster base default image id or specific one from node group

Change-Id: I141110fbe1ba9dbc2f82d5748af6cd8643c411ee
Small code improvements.

* avoid None iteration in configs util
* display instances in cluster details
* display more info while provisioning cluster

Change-Id: I33026468911a3f93695468cde8d67db02485a77a
Merge "Core part improvements."
Merge "Small code improvements."