Also use indexing for DPIDs to avoid zeroed MAC

Auto MAC setup sets each host MAC equal to its DPID, which simplifies
debugging.

Auto ARP setup removes the need for broadcast support for ARP, which
enables a smaller NOX controller.

If ripcord.dctopo imports properly, then include its topologies in the
list of available ones.  Also replace topo.py with new generic
topologies and update paths.

Also simplify test running.

Also remove usused imports and outdated doc text.

Simplifies launching a Mininet or running tests on one.