fix: child image should be rebuildable

The Filter function constructs a completely new graph were unmodified images
are discarded. I suppose it was done to have a (very) smaller graph to improve
(a little) performance.

Unfortunately, we need info on all direct parents images when rebuilding, at
least to properly amend the FROM line to be able to pull the right parent
image. Thus this refacto broke completely rebuild of every image with at least
one not-to-rebuild parent.

I fix this quickly by avoiding the Filter function altogether which is too
complicated for our sake and does not really improves the performances.

Fixes be5509e

pkg/dib/build.go

@@ -83,13 +83,13 @@ func (p *Builder) rebuildGraph(
 	buildArgs map[string]string,
 ) {
 	p.Graph.
-		Filter(
-			func(node *dag.Node) bool {
-				return node.Image.NeedsRebuild || node.Image.NeedsTests
-			}).
 		WalkParallel(
 			func(node *dag.Node) {
 				img := node.Image
+				if !(img.NeedsRebuild || img.NeedsTests) {
+					img.RebuildFailed = false
+					return
+				}
 				buildReport := report.BuildReport{Image: *img}
 
 				// Return if any parent build failed