Split cluster.py

cluster.py is nearly 4000 lines long and consists of two independent
parts: on one hand there is everything related to verifying the cluster
and there is everything else.

This change moves everything from cmdlib/cluster.py to either
cmdlib/cluster/__init__.py or cmdlib/cluster/verify.py.

Signed-off-by: Aaron Karper <akarper@google.com>
Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>
Reduce maximal module size

This patch reduces the max-module-size of the project to 3600, which is
slightly larger than the currently largest module (baring backend.py,
which got a free pass): config.py

In an efford to reduce the module size to something more reasonable, the
next person to hit the wall will find a nice reminder: Please reduce the
maximal module size further when possible.

Signed-off-by: Aaron Karper <akarper@google.com>
Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>