This adds a new optional (so we're backwards-compat) section to the
cluster data so that we can reliably save/restore the policy data.

Note that different from the other sections, we save all policies
together and separately from the group data. I thought this is cleaner
than extending adding the policy data near each group, and a new
section just for the cluster policy.

This change also allows simplification of the unittest for cluster
create/serialize, although we would need a more complete test (right
now we only dump/load the defIPolicy or nullIPolicy).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>