unit tests fixed by fixing an archipelago bug. A cluster is a *strongly...

unit tests fixed by fixing an archipelago bug. A cluster is a *strongly connected* group of switches. A switch that is weakly connected to a cluster but not strongly connected to any other cluster will exist in its own cluster. This weak link, if not an external/BDDP-discovered link, will not be used to try and compute paths. Thus, while we compute clusters, any link that is not within a cluster and is not an external link is stored for reference when computing archipelagos. Essentially, the external links which typically are between clusters get merged into a new set with these weak links to allow for proper computation of archipelagos.