Add nodetypeXpid_permissions table, which indicates what projects are
allowed to allocate a node type. An entry in this table means the type is restricted; no entries means the type is unrestricted. Add "isvirtnode" slot to node_types table so that we can put in entries like pcvron, pcvroninet2, etc. Various parts of the testbed software will check this flag. Add phys_nodeid slot to nodes table, which maps a virtnode to its physical nodes (vron23 maps to ron3). Set phys_nodeid=node_id for normal testbed nodes. Change type of priority in the nodes table to a plain int (from smallint) since I added a bunch of nodes and spread the priority numbers out pretty far.