Remove import of 'imp' module

[Rodolfo Alonso]

Use importlib.util module instead of imp, since it's
being deprecated:

  DeprecationWarning: the imp module is deprecated in favour of
  importlib; see the module's documentation for alternative uses

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

WIP patch: https://review.opendev.org/c/openstack/neutron/+/842450

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/842450
Committed: https://opendev.org/openstack/neutron/commit/357ee21d12d0af6c64ba60f541ab61d44cd6d00f
Submitter: "Zuul (22348)"
Branch: master

commit 357ee21d12d0af6c64ba60f541ab61d44cd6d00f
Author: Brian Haley <email address hidden>
Date: Wed May 18 21:38:06 2022 -0400

    Remove import of 'imp' module

    Use importlib.util module instead of imp, since it's
    being deprecated:

      DeprecationWarning: the imp module is deprecated in favour of
      importlib; see the module's documentation for alternative uses

    Had to change test setup to call super() first to get around a
    config issue I was seeing locally, causing the entire class of
    tests to fail:

      oslo_config.cfg.NoSuchOptError: no such option api_extensions_path
      in group [DEFAULT]

    Closes-bug: #1981077

    Change-Id: Ic171028a661c3f9f83f6758a57aaeab4450aa907

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 21.0.0.0rc1 release candidate.