pep8 error caused by hacking version < 3.0.1

[Brin Zhang]

flake8 new release 3.8.0 added new checks and gate pep8
job start failing. hacking 3.0.1 fix the pinning of flake8 to
avoid bringing in a new version with new checks.

Though it is fixed in latest hacking but 2.0 and 3.0 has cap for
flake8 as <4.0.0 which mean flake8 new version 3.9.0 can also
break the pep8 job if new check are added.

To avoid similar gate break in future, we need to bump the hacking min
version.

- http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014828.html

https://review.opendev.org/#/c/727347/ changing the hacing version, but some related error in the code, see below:

pep8 run-test-pre: PYTHONHASHSEED='1704528896'
pep8 finish: run-test-pre after 0.00 seconds
pep8 start: run-test
pep8 run-test: commands[0] | bash tools/flake8wrap.sh
setting PATH=/home/zuul/src/opendev.org/openstack/nova/.tox/shared/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
[4453] /home/zuul/src/opendev.org/openstack/nova$ /bin/bash tools/flake8wrap.sh
Running flake8 on all files

./nova/tests/unit/virt/vmwareapi/test_driver_api.py:126:14: H202: assertRaises Exception too broad
./nova/tests/unit/compute/test_compute_mgr.py:6264:9: E306 expected 1 blank line before a nested definition, found 0
./nova/api/openstack/compute/servers.py:104:23: E741 ambiguous variable name 'l'
./nova/db/sqlalchemy/migrate_repo/versions/330_enforce_mitaka_online_migrations.py:48:35: E711 comparison to None should be 'if cond is None:'
ERROR: InvocationError for command /bin/bash tools/flake8wrap.sh (exited with code 1)
pep8 finish: run-test after 70.95 seconds
pep8 start: run-test-post
pep8 finish: run-test-post after 0.00 seconds
___________________________________ summary ____________________________________
ERROR: pep8: commands failed

[Ghanshyam Mann (ghanshyammann)]

hacking 3.0.0 is fixed with new version bump - https://review.opendev.org/#/c/727347/1

we can adopt hacking 3.1.0 as min version and adopt the new checks.

[Brin Zhang (zhangbailin)]

https://review.opendev.org/#/c/727589/8 this patch bumped hacking min version to 3.1.0, and fixed these pep8 issue.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/727589
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=61b99a1295c5208deef806b69ba74a7d031ad851
Submitter: Zuul
Branch: master

commit 61b99a1295c5208deef806b69ba74a7d031ad851
Author: zhangbailin <email address hidden>
Date: Wed May 13 10:15:20 2020 +0800

    Bump hacking min version to 3.1.0

    This has introduced a new version of pycodestyle, which has improved its
    parser to catch new corner cases and introduced some new tests.

    Closes-Bug: #1878317
    Change-Id: I853cf4dbd7ad6b7903a7f444f5c1da3f0fb21f77

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/ussuri
Review: https://review.opendev.org/c/openstack/nova/+/768197
Reason: stable/ussuri branch of openstack/nova transitioned to End of Life and is about to be deleted. To be able to do that, all open patches need to be abandoned.