Graph component auto-executing subgraphs.

When the `Graph` component is used as a subgraph the contained graph is executed despite the fact that the `start` port has been removed via `ComponentLoader` on line 161: https://github.com/noflo/noflo/blob/3068b0e81af1c775f4c4b4df350717d961e8aac4/src/lib/ComponentLoader.coffee#L161
