Add rootfs service

Add rootfs service to allow creation of rootfs from layer array

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

cmd/containerd/builtins.go

@@ -7,6 +7,7 @@ import (
 	_ "github.com/docker/containerd/services/execution"
 	_ "github.com/docker/containerd/services/healthcheck"
 	_ "github.com/docker/containerd/services/metrics"
+	_ "github.com/docker/containerd/services/rootfs"
 	_ "github.com/docker/containerd/snapshot/btrfs"
 	_ "github.com/docker/containerd/snapshot/overlay"
 )