sync cluster task not running with send cluster metrics enabled

[Ricardo Rocha]

After upgrading to Pike, we noticed the sync of the cluster status (from the Heat stacks) stopped working. Cluster creation creates a stack, but once it goes to STACK_COMPLETE the Magnum cluster status remains CREATE_IN_PROGRESS.

After some debugging, we ended up disabling the send_cluster_metrics periodic task directly in the code, which seems to be the cause of the problem. It's ok as we don't rely on this to collect metrics, but there's no easy way to disable individual tasks so it needs a proper fix.

For information we rely on Barbican to manage cluster certificates, which might be a hint as it's a difference to the usual devstack setup.