Legacy EngineFacade was deprecated a while ago, using new
EngineFacade system is the recommended way to work with
db engine and session.
The new system has a lot of notable changes[1]:
* Thread-safe initialization of EngineFacade;
* Declarative reader/writer transactions separation;
* Transaction scope defined by developer-specified context.
[1] http://specs.openstack.org/openstack/oslo-specs/specs/kilo/make-enginefacade-a-facade.html
Closes-Bug: #1475182
Change-Id: Ia03f35a1f3b22b2eda74263e319469cf2391e7b5