Adds multi-region support for stack resource

Adds new resource type called OS::Heat::Stack which allows
creating new stack in specified region using heatclient.

Implements: blueprint multi-region-support

Co-Authored-By: Qiming Teng <tengqim@cn.ibm.com>

Change-Id: I62cb07877702c57dd0e77dbcb0e123a3ec2c885d
Merge "Adds multi-region support for stack resource"