Take no dry run in: mark it on the request, echo it on the outcome, set it aside

A dry run of an unreviewed branch was heard by the daemon like any build, registered, and its
definition reached a machine (novox/hq issue 240). The mark now travels with the build and the
daemon records, registers and plans nothing for it.

cmd/mesh-builder/main.go

@@ -171,7 +171,7 @@ func answer(ctx context.Context, publisher builder.Publisher, on, workspace stri
 
 	result := link.BuildResult{
 		ID: request.ID, Repository: request.Repository, Path: request.Path,
-		Ref: request.Ref, On: on, Source: request.Source,
+		Ref: request.Ref, On: on, Source: request.Source, DryRun: request.DryRun,
 	}
 	what := "building " + request.Repository
 	if request.Path != "" {