Update config.sh

HA deployment on ubuntu with 3 nodes: 1 controller, 1 compute and 1 zabbix fails with "Deployment has failed. Timeout of deployment is exceeded." because of swapping. So, propose to update comment about minimum ubuntu RAM.

VERSION:
  feature_groups:
    - mirantis
    - experimental
  production: "docker"
  release: "5.1"
  api: "1.0"
  build_number: "11"
  build_id: "2014-09-17_21-40-34"