Unit tests fail due to unsupported .removeprefix() in python 3.7

[Roman Krček]

Description
===========
When running unit tests on python3.7 two tests fail:
nova.tests.unit.console.test_websocketproxy.NovaProxyRequestHandlerBaseTestCase.test_reject_open_redirect
nova.tests.unit.console.test_websocketproxy.NovaProxyRequestHandlerBaseTestCase.test_reject_open_redirect_3_slashes

Steps to reproduce
==================
Checkout to latest stable/train as of 17.08.2023
$ tox -e py37

Expected result
=============
All unit tests pass

Actual result
=============
`Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/builds/nfv-platform/nova/nova/tests/unit/console/test_websocketproxy.py", line 678, in test_reject_open_redirect'
    b" location = location.removeprefix('Location: ').rstrip('\\r\\n')"
    b"AttributeError: 'str' object has no attribute 'removeprefix'"
    b''`

`Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/builds/nfv-platform/nova/nova/tests/unit/console/test_websocketproxy.py", line 685, in test_reject_open_redirect_3_slashes'
    b" self.test_reject_open_redirect(url='///example.com/%2F..')"
    b' File "/builds/nfv-platform/nova/nova/tests/unit/console/test_websocketproxy.py", line 678, in test_reject_open_redirect'
    b" location = location.removeprefix('Location: ').rstrip('\\r\\n')"
    b"AttributeError: 'str' object has no attribute 'removeprefix'"
    b''`

Environment
===========
Python version 3.7.17

[Roman Krček (r-krcek)]

This issue was introduced with the following commit https://review.opendev.org/c/openstack/nova/+/866201

[Takashi Kajinami (kajinamit)]

I believe this bug is invalid because Python 3.7 is no longer supported. You should use Python 3.8 or later.

https://github.com/openstack/nova/blob/master/setup.cfg#L13

See https://governance.openstack.org/tc/reference/runtimes/ to find out the python versions supported by each release.

[Roman Krček (r-krcek)]

Sorry if I didn't specify it correctly, but I was referencing Train release in this bug report which should use python 3.6 or 3.7 as the default version. However, even updating to Python 3.8 would not help, since .removeprefix() wasn't implemented until Python 3.9. So most releases using Python 3.8 and Python 3.7 are affected.

This bug results from a change, which was introduced as a result of the following bug report https://bugs.launchpad.net/nova/+bug/1986545

After a lot of searching, I was, in the end, able to find a commit to master that fixed this issue https://opendev.org/openstack/nova/commit/3ccf82ef9e2c87a1d33a0dda8929c05e80844087

[Sylvain Bauza (sylvain-bauza)]

As said, triaging as Valid as https://review.opendev.org/c/openstack/nova/+/867788 requires backports.

[melanie witt (melwitt)]

https://review.opendev.org/c/openstack/nova/+/867788 proposed to stable/zed