openvswitch: include Python setuptools for tests

Fixes test(s) that fail with the following output:

```
2611: Pytest unit tests - Python3                     ok

ERROR: 2600 tests were run,
1 failed unexpectedly.
12 tests were skipped.

Please send 'tests/testsuite.log' and all information you think might help:

   To: <bugs@openvswitch.org>
   Subject: [openvswitch 3.3.0] testsuite: 2531 failed

You may investigate any problem if you feel able to do so, in which
case the test suite provides a good starting point.  Its output may
be found below 'tests/testsuite.dir'.

Traceback (most recent call last):
  File "<string>", line 4, in <module>
ModuleNotFoundError: No module named 'pkg_resources'
```