Ironic notifications for bare metal DM

For a data center with large amount of VMs and physical hosts,the total power consumption is tremendous.
When workload is not heavy, Watcher can be used to reduce power consumption by triggering a request to power off some idle hosts without VMs.
And when the workload increases watcher will trigger a "power on" request to fullfill the service requirements.

This feature includes four sub-features:
1) Build a new baremetal (ironic) data model within current Watcher Cluster Data Model
2) Add new actions "power on" and "power off" in Watcher
3) Implement a new strategy based on 'baremetal' and 'compute' data models, which could trigger 'compute' and 'baremetal' actions.
4) Update the bare metal data model by ironic notifications

This BP implements the fourth sub-feature: Update the bare metal data model by ironic notifications.