This adds some attributes for adjusting the thread counts for each wsgi
application. By default we use 10 threads, however for the api service, it needs
to be set to 1 due to this upstream issue [1]. In addition, increase the
processes for the api service to 6 to account for the reduction in threads.

[1] https://docs.openstack.org/releasenotes/nova/stein.html#known-issues

Change-Id: Iebf78d24c57a069eabced1bf35051cbae5014902