Refactor,update images

  * Switch ubuntu|salt-stack to fetch from mirror.mirantis.com/proposed
  * ubuntu-16-04 - add openstack builder[inactive stub]
  * add info.sh - and enable it in mirror and ubuntu16
  * Drop mcp salt repos - we don't use them for build
  * switch to release-20180306 ubuntu cloud image

Change-Id: Ic45db3fd2579262b055ecdc54b27a16a837c2dd4
10 files changed