Rough design overview.

There are 4 parts planned:

+------------+    +---------------+
|snake-server|    |snake-scheduler|
+------------+    +---------------+
      |    server-side     |
------+--------------------+-------
      v    client-side     |
+------------+       +------------+
|snake-client|------>|snake-daemon|
+------------+       +------------+

Currently, we have two parts (mostly) functioning:

snake-server is the XMLRPC server that provides information about available
trees, ISO sets, etc.

snake-client is an XMLRPC client that uses information from snake-server to
perform installations.


In the future, we will have:

snake-daemon, which runs on client machines that are available for fulltime
installation testing, and

snake-scheduler, which keeps track of machines running snake-daemon and tells
them which tree to install from.
