Remove "distutils" library
Remove "distutils" library

Library "distutils" will be marked as deprecated in Python 3.10:
https://peps.python.org/pep-0386/

This patch does the following replacements, that provide the same
functionality and API:
- distutils.spawn.find_executable -> shutil.which

Change-Id: Ib9cf36a70b6e5aba93f87e6be5c2636599166de2
Closes-Bug: #1973780

openstack/neutron-fwaas,openstack/neutron-fwaas