RecipeUpstreamHistory was not linked to the layer it was produced from,
which meant that it wasn't easy to query for a different maintenance
plan (i.e. a different layer) and thus the maintenance plan selection
on the recipe list didn't really work. Add a link field, populate it in
a migration and then make it required.
We had added a link earlier from RecipeMaintainerHistory to LayerBranch
but it was optional; for the same reasons we now populate it and make it
required.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
