SPEC-2962: permit to have more than one board per build

SPEC-2962: permit to have more than one board per build

The current way to generate jobs assume that only one board exists per
build.

For handing more than one board per build, we need to introduce a sort
of loop.

So for each build, we will produce a list of boards in BOARDOUT
In the BOARDOUT/$board, we will have:
- an "info" file with all necessary VARIABLES for copying artifacts

So for each board, some artifact will be copied.

Then only one job for the "main" board of the CIBT job will be handled.
The extra boards of a build will need to have their own CIBT, but at
least they dont need to do a real build/copyartifact.

Change-Id: I6c6999e549c7f1216f466410896b3058efc5882d
Signed-off-by: Corentin LABBE <clabbe@baylibre.com>