Added a view to ganetiviz - ClusterJsonView that returns all cluster data at once.
(Reduces number of hits to the database)

Refs #13569
ganetiviz performance optimization
- Solved an issue in ClusterJsonView in ganetiviz which returns all cluster data
- Changed templates, JS code to use updated JSON format

Refs #13569
Enhancements and a bug correction in abstract-graph-modelling.js code in ganetiviz
(Bug was new, due to the adoption of new nodes, vms combined JSON format)