Bug 9588

Create "build descriptor" that is in a format such as yaml that is only a description of the items needed to define a build and it's output.

This information will include items such as configuration that would normally be in places such as local.conf, layers that would be in bblayers.conf and possibly build artifacts that are *important* such as an image file or sdk.

This should be written in a consumption agnostic way, i.e. the language definition doesn't care who is consuming it outside of that it is machine consumable.

Some examples of consumers would be autobuilder, jenkins, toaster, command line, etc. The idea is that knowing the descriptor specification allows anyone to write a consumer that will perform the necessary steps to create a build.