Make default node 2+ directory paths derived from node 1's directory

For deon's use with Docker:
When creating new nodes (after node 1), derive the new node directory from node 1's configured directory if possible (e.g. it has a '1' in it). So if Node 1's directory is /blah/bbsdir1, then node 2's directory will default to /blah/bbsdir2. When creating node 1 (the first node), it still defaults to "../node1".