python3: func_doc was renamed to __doc__

[Lajos Katona]

testing on python3 the following error messages appear in the logs:
ERROR oslo_service.service [None req-2ddf2e60-9f22-4700-a0cc-203bb56e3828 None None] Error starting thread.: AttributeError: 'function' object has no attribute 'func_doc'

See the code:
https://opendev.org/openstack/networking-odl/src/commit/5177658d8bad4d97444519ef21fe024629954b71/networking_odl/journal/periodic_task.py#L58

And the relevant change log for python:
https://docs.python.org/3.0/whatsnew/3.0.html#operators-and-special-methods

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/683152

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/683152
Committed: https://git.openstack.org/cgit/openstack/networking-odl/commit/?id=924141c66354d4b165cc02402fa5a6b092a97c4e
Submitter: Zuul
Branch: master

commit 924141c66354d4b165cc02402fa5a6b092a97c4e
Author: elajkat <email address hidden>
Date: Thu Sep 19 15:08:50 2019 +0200

    Change function.func_doc to function.__doc__

    In python3 func_doc was renamed to __doc__, see [0].

    [0]: https://docs.python.org/3.0/whatsnew/3.0.html#operators-and-special-methods
    Closes-Bug: #1844660

    Change-Id: I8585f8429acb7359e1f372a5e4f378ca5ce6b540

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/networking-odl 16.0.0.0b1 development milestone.