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-controller/build.go

@@ -592,6 +592,7 @@ func buildAndShow(ctx context.Context, source buildSource, path, ref string, wai
 		ID:         link.NewBuildID(time.Now()),
 		Repository: repository, Path: path, Ref: ref,
 		Held: heldBy(ctx), Seats: seatBases(ctx),
+		DryRun: true,
 	}, wait)
 	if err != nil {
 		return err