Add the ability to Kolla-ansible to manage the 'max_workers' parameter
in Cloudkitty. We will use the 'openstack_service_workers' variable
to control the number of workers that Cloudkitty is able to use.
Change-Id: I2f4e7e5c45d71a7e01d1b743d2eb4850cc339419
Signed-off-by: Rafael Weingärtner <rafael@apache.org>