Database model for software config/deployment

These database tables act as storage to SoftwareConfig
and SoftwareDeployment entities which are exposed via the
heat REST API.

There is no software_config_update as software config entities
are immutable after creation. This allows them to be created
outside any stack which uses them, and used by reference without
being concerned about their contents changing over time.

Implements: blueprint hot-software-config-rest
Change-Id: I9ff17f48dcd9605ff76f81007c559596234eac6e
Merge "Database model for software config/deployment"