Add diskimage-builder script for Drone

Beginning of the work on the build-farm

Part of blueprint solum-build-farm
https://blueprints.launchpad.net/solum/+spec/solum-build-farm

Change-Id: I77bc72c39d73e8d5a0d3d84baa970acea2e668c5
Merge "Add diskimage-builder script for Drone"