Refactor display of cluster template

Change-Id: Ie3f85420461ab9f5b5d5f8565bd68dbbd6257dad
Implements: blueprint python-savannaclient-cli
Refactor display of cluster

Change-Id: I3b8cfc9c91af300a22b14963f82ec372c416ad41
Implements: blueprint python-savannaclient-cli
Add --json option to node-group-template-show

Allows for exporting of node group template in a JSON representation

Change-Id: I98e991f62bdcc97c374722f364268700471fb9a3
Implements: blueprint python-savannaclient-cli