Key updates to the "Scalability Testing and Tuning" Guide

For those of you running large-scale deployments, we have updated the “Scalability Testing and Tuning” guide with a new section about how to scale the API server by balancing client requests across multiple “oned” processes.

http://docs.opennebula.org/5.8/deployment/references/one_scalability.html#scaling-the-api-server