Permit larger database connection count
Permit larger database connection count

The default incoming database connection count is limited to 151
connections.  These are not sufficient in a 100 node 3 controller
deployment to launch several heat stacks simulatenously.

Data measured on bare metal shows that 250 connections are needed
to launch one 25 VM heat stack with 3 controller nodes with 209
tasks (default enablement).

Change-Id: If60b540010d6d173a393fa91fa30cb3ba572cfc0
Closes-Bug: #1492719

nihilifer/kolla,stackforge/kolla,fdumpling/kolla,intel-onp/kolla,rajalokan/kolla,dardelean/kolla-ansible,stackforge/kolla,rahulunair/kolla,tonyli71/kolla,limamauricio/mykolla,mandre/kolla,fdumpling/kolla,fdumpling/kolla,GalenMa/kolla,limamauricio/mykolla,toby82/kolla,nihilifer/kolla,mrangana/kolla,dardelean/kolla-ansible,negronjl/kolla,tonyli71/kolla,openstack/kolla,mandre/kolla,toby82/kolla,negronjl/kolla,GalenMa/kolla,rajalokan/kolla,mandre/kolla,limamauricio/mykolla,coolsvap/kolla,dardelean/kolla-ansible,mrangana/kolla,stackforge/kolla,coolsvap/kolla,intel-onp/kolla,negronjl/kolla,rahulunair/kolla,toby82/kolla,coolsvap/kolla,openstack/kolla,rajalokan/kolla