Comment 2 for bug 1959925

Reviewed: https://review.opendev.org/c/starlingx/utilities/+/827755
Committed: https://opendev.org/starlingx/utilities/commit/5872b851ec2fc2fafabba7b9a35e6ca4ded586e7
Submitter: "Zuul (22348)"
Branch: master

commit 5872b851ec2fc2fafabba7b9a35e6ca4ded586e7
Author: Heitor Matsui <email address hidden>
Date: Thu Feb 3 15:33:55 2022 -0300

    Create libvirt connection on NovaProvider constructor

    Before I58cefac9076db52333b41633bf2cbaa5441dc98c the Nova client
    was created on nova_provider module and imported by other modules
    as a single and shared instance, and it's libvirt connection was
    created once during the agent.process_main function execution if
    OpenStack was enabled.

    Now with the Nova client being created on-demand during the agent
    operation, the libvirt connection opening isn't behaving well inside
    threads and is returning an empty object when called.

    This commit makes the libvirt connection to be opened when the
    NovaProvider instance is created and closed when it is destroyed,
    and return to a similar behavior before the refactor, but now by
    creating a singleton NovaProvider instance on the main thread
    that will be used by other modules during the agent execution,
    preventing unnecessary code execution during nova_provider import.

    Test Plan:
    PASS: Create an instance with SRIOV or PCI-PT and verify that
          instance CPU cores are affined to the PCI device IRQs
    PASS: Verify that log shows no more warnings and errors related
          to domain information retrieval on libvirt

    Closes-bug: 1959925
    Change-Id: Ie72ccca5b63e1a984233703ed518f26564d67dd7
    Signed-off-by: Heitor Matsui <email address hidden>