heat engine changes for abandon-stack

abandon-stack operation is similar to delete-stack, but actual
resources would not be deleted. Only stack and resource data
would be deleted from heat database. And also abandon-stack
operation would return the stack/resources data in json format.

Implements: blueprint abandon-stack
Change-Id: Ibb386255887d4de54e9a3dc95254a7151475cf3a
contrib: Add Docker Container plugin

This plugin enable using Docker containers as
resources in a Heat template.

Change-Id: Id9fd6c3491b246c88308713a7661be1ad0056eb5
Implements: blueprint docker-plugin
Merge "heat engine changes for abandon-stack"
Merge "contrib: Add Docker Container plugin"