Implementation of the SoftwareConfig resource. Some notes on the implementation:
* This is a simple wrapper over the REST API, and is essentially
just for defining data which gets stored.
* SoftwareConfig will always be UpdateReplace, and the REST entity
is immutable.
* OS::Heat::SoftwareConfig will sometimes be used in a template directly
and sometimes inside a resource provider template which
defines CM-tool specific properties and aggregates the result into
the OS::Heat::SoftwareConfig config property.
Implements: blueprint hot-software-config
Change-Id: I7350c31ec59d152751c6aa7d811a91e1df62e89d
21f60b155e