Increase database connections to 10000
Increase database connections to 10000

Scale limit testing on a 64 node cluster with 13 TB RAM and 2600
cores showed that atleast 1800 database connections are required
to appropriately start 2000 virtual machines simulateounsly.  Other
documentation on the internet recommends larger values such as 8000,
so we set to a larger value that should be able to handle a maxed out
512GB ram per compute node cluster with all services enabled.

Change-Id: I8767cf3fb04e066cc22e796c647e944b4e4a1742
Closes-Bug: #1564275
(cherry picked from commit 1fac190cec3c628c8a4c745659fcec090d952abd)

negronjl/kolla,negronjl/kolla,negronjl/kolla