Alarms default to node['cloud_monitoring']['notification_plan_id']

We got tired of putting this everywhere and figured this was a
sensible default.
Sanity check the presence of notification_plan_id.
Bump version to 0.2.1
Merge pull request #22 from racker/make_notification_plan_default_to_data_bag

Alarms default to node['cloud_monitoring']['notification_plan_id']