Add --json option to cluster-show
Add --json option to cluster-show

Allows for exporting of cluster in a JSON representation

Change-Id: I37645fcc3afaeb1792fd4be2962603aeff04a6c1
Implements: blueprint python-savannaclient-cli

openstack/python-saharaclient,citrix-openstack-build/python-saharaclient,citrix-openstack-build/python-saharaclient,citrix-openstack-build/python-saharaclient