Added new tests for Heat component.

- test_heat.py: added tests for stack rollback and autoscaling;
- heatmanager.py: added new accessory methods;
- test_sanity_heat.py: minor update per changes in heatmanager.py;
- config.py: removed unused Heat option;
- nmanager.py: modified endpoint in _get_heat_client,
  little enhancement in _create_flavors method to avoid issue
  with wrong param. values assignment.

Platform tests description that is mentioned in autoscaling
test script is also under review at the moment:
https://review.openstack.org/#/c/61115/

Change-Id: Ie860c155f3fc5f8b54eccd39e673f59e04d40b0b
Merge "Added new tests for Heat component."