uuidsentinel does not follow __getattr__ protocol

[Balazs Gibizer]

uuidsentinel raises a ValueError if called __getattr__ called with an attribute starting with '_' This breaks the getattr protocol by making getattr() builtin to raise instead of return the value of the default args. This breaks nova unit test under mock 4.0.x [1].

The proper exception would be an AttributeError as stated by [2]

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=963339
[2] https://python-reference.readthedocs.io/en/latest/docs/dunderattr/getattr.html#remarks

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/738207

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/738207
Committed: https://git.openstack.org/cgit/openstack/oslo.utils/commit/?id=bc562f3393e976e7086642f03ef62a914a9b2dcc
Submitter: Zuul
Branch: master

commit bc562f3393e976e7086642f03ef62a914a9b2dcc
Author: Balazs Gibizer <email address hidden>
Date: Fri Jun 26 15:34:52 2020 +0200

    Fix uuidsentinel to follow getattr protocol

    This patch changes the exception type raise by uuidsentinel when the
    sentinel name starts with '_'. The __getattr__ protocol requires to
    raise an AttributeError if the attribute value cannot be returned.

    Closes-Bug: #1885281
    Change-Id: I1076a957a19507e7d96ef429c0ae5d0ee8a90e66