Update nova::config example description.

The original example in nova::config is syntax invalid.
Besides fixing that, this patch also gives an example in yaml format.

Change-Id: I2f044392becd9e46cc8346030095a029464c5ea0
Closes-bug: #1301700
Improve notifications parameters

Reasons:
- The monitoring_notifications parameter is old and only valid for
stable/essex.
- We need to change the driver and topics notification
- We need to notify on VM or/and task state changes

Changes:
- Add notification_driver option
- Add notification_topics option
- Add notify_api_faults option
- Add notify_on_state_change option

Change-Id: I9d1c5c57a4a5f805e174390d53a0f54319b16c79
Merge "Improve notifications parameters"
Merge "Update nova::config example description."