Set default of api_workers to number of CPUs

[OpenStack Infra]

https://review.openstack.org/140493
commit c65175811baf29e75556045e3b44ab948e02a9c3
Author: Russell Bryant <email address hidden>
Date: Tue Dec 9 14:59:20 2014 -0700

    Set default of api_workers to number of CPUs

    The current default for api_workers is 0. This patch changes it to
    use the number of CPUs available, which is the default that will
    provide best performance. This is consistent with some other
    OpenStack service (Nova and Swift, at least, perhaps others).

    Note that devstack is updated in another patch to ensure multiple API
    workers is being tested for Neutron the same way it's tested for
    several other services:

        https://review.openstack.org/140482

    Co-Authored-By: Eugene Nikanorov <email address hidden>
    DocImpact
    UpgradeImpact
    Change-Id: I4d76baf68b014fc80693f53874734783089abda2

[Tom Fifield (fifieldt)]

added release note: https://wiki.openstack.org/wiki/ReleaseNotes/Kilo#Upgrade_Notes

[Tom Fifield (fifieldt)]

https://review.openstack.org/#/c/177283/