Adds Support for Heat's Database Idle Timeout

Requires the following Heat patch:
  https://review.openstack.org/#/c/78007/

Previously, stack builder's full_ha scenario would configure a
30-sec idle timeout for all services except Heat.  This patch
aligns Heat with other OS services idle timeout configuration.

Change-Id: I70b32f6c02331c8acfd87dc6692df328d628f6b8
Merge "Adds Support for Heat's Database Idle Timeout"