Add instance_usage_audit parameters

Reasons:
- We must allow the generation of periodic compute.instance.exists
notifications

Changes:
- Add instance_usage_audit parameter
- Add instance_usage_audit_period parameter

Change-Id: I9e10dfb2a32edb80a82eec564dfda045fa25bbc7
Merge "Add instance_usage_audit parameters"
Merge git://github.com/puppetlabs/puppetlabs-nova