Add ONBUILD support to --change

Return types had to change a bit for this, but since we can wrap
the old v1.ImageConfig, changes are overall not particularly bad.

At present, I believe this only works with commit, not import.
This matches how things were before we changed to the new parsing
so I think this is fine.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/container_commit.go

@@ -183,6 +183,9 @@ func (c *Container) Commit(ctx context.Context, destImage string, options Contai
 	if newImageConfig.StopSignal != "" {
 		importBuilder.SetStopSignal(newImageConfig.StopSignal)
 	}
+	for _, onbuild := range newImageConfig.OnBuild {
+		importBuilder.SetOnBuild(onbuild)
+	}
 
 	candidates, _, _, err := util.ResolveName(destImage, "", sc, c.runtime.store)
 	if err != nil {