Fix DeleteNode problems that Mike caused, oops I mean experienced.

Two problems that @hibler ran into:

1. On a simple lan of nodes, linktest worked before deletenode, but failed after a successful deletenode. See https://www.emulab.net/showslicepub.php?publicid=4323798adf514aedff6d95208ccd36de

2. On a full mesh topology, DeleteNode() failed miserably leaving things in a funky state. See https://www.emulab.net/showslicepub.php?publicid=b2b3b121bb5e30f5b80bc198fd57d12a