knockouts: Fill empty zones with None

Some of the knockout matches have fewer than 4 teams in them.  This
makes sure that the empty zones for those matches are filled with None
as appropriate.
Put the last N rounds in a given set of arenas

To maximise suspense, and excitement, put the last few rounds in the
same arena.  New config options are required for this.
knockouts: Add a simple random shuffler

This shuffles the teams zones in the knockouts.  Done using an LFSR,
which is seeded by the md5 of the seeded team list.
stable_random: Allow running from cli

Will generate 10 numbers then exit.  Will be useful in a moment for
verifying this is stable across machines etc.
Bump submodule so it's valid again.

Adds the single_arena key.

Change-Id: I8454a7a53cc15438443d5ece1150c1a5f751296e