Change OpClusterVerifyConfig's result, verify results

This patch removes the list of node groups (not used anymore since
commit fcad7225) from OpClusterVerifyConfig's result and adds result
verification to all OpClusterVerify* opcodes.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>