Improve get optimal count of max_worker for pool

[Chenjun Shen]

In the upstream of futures library, the DEFAULT value max_worker for ThreadPoolExecutor and ProcessPoolExecutor has been changed to:

ThreadPoolExecutor

max_worker = cpu_count() * 5

Reference:
https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/thread.py#L109

ProcessPoolExecutor

max_worker = cpu_count()

Reference:
https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/process.py#L278

So we should do it as well.

[Chenjun Shen (cshen)]

Patch is here.

https://review.openstack.org/#/c/529082/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/529082
Committed: https://git.openstack.org/cgit/openstack/futurist/commit/?id=8fff2242ff53735255247a1b126727e374fe9159
Submitter: Zuul
Branch: master

commit 8fff2242ff53735255247a1b126727e374fe9159
Author: Chenjun Shen <email address hidden>
Date: Tue Dec 19 15:19:56 2017 +0100

    Improve get optimal count of max_worker for pool

    In the upstream of futures library, the DEFAULT value max_worker
    for ThreadPoolExecutor and ProcessPoolExecutor has been changed to:

    ThreadPoolExecutor

    max_worker = cpu_count() * 5

    Reference:
    https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/thread.py#L109

    ProcessPoolExecutor

    max_worker = cpu_count()

    Reference:
    https://github.com/agronholm/pythonfutures/blob/master/concurrent/futures/process.py#L278

    So we should do it as well.

    Change-Id: Id68e38a639c41426f125180ad335fb1fb97cba59
    Closes-bug: #1739034

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/futurist 1.6.0 release.