Major Description
Today when we group processor nodes into groups (i.e. sub-topologies), we assign the sub-topology id for global tables' dummy groups as well. As a result, the subtopology ids (and hence task ids) are not consecutive anymore. This is quite confusing for users trouble shooting and debugging; in addition, the node group for global stores are not useful as well: we simply exclude it in all the caller functions of makeNodeGroups.
It would be better to simply exclude the global store's node groups in this function so that the subtopology ids and task ids are consecutive.
