Fix python(abi) generator (the one written in Python)

There were three problems:

 - sys.version was not imported
 - sys.version[:3] is not reliable on Python 3.10+
 - distutils is deprecated on Python 3.10+

We were not hit by the missing import in Fedora because we only run the script
on .dist-info/.egg-info/.egg and not on .py files, so this if-branch never runs.

But when the script was fed with a .py path, it errored:

    Traceback (most recent call last):
      File "/usr/lib/rpm/pythondistdeps.py", line 344, in <module>
        purelib = get_python_lib(standard_lib=0, plat_specific=0).split(version[:3])[0]
    NameError: name 'version' is not defined

The sys.version[:3] thing kinda works for Python 3.10+ because *in this
particular case* splitting on '3.1' and taking the prefix yields the same
results as splitting on '3.10', but I consider that mere coincidence.

Finally, since the distutils import happened at module-level,
we got the Deprecation warning in all Fedora's Python packages:

    /usr/lib/rpm/pythondistdeps.py:16: DeprecationWarning: The distutils package is deprecated and slated for removal in Python 3.12

Backported from d12e039037

python-rpm-generators.spec

@@ -1,7 +1,7 @@
 Name:           python-rpm-generators
 Summary:        Dependency generators for Python RPMs
 Version:        12
-Release:        5%{?dist}
+Release:        6%{?dist}
 
 # Originally all those files were part of RPM, so license is kept here
 License:        GPLv2+
@@ -47,6 +47,11 @@ install -Dpm0755 -t %{buildroot}%{_rpmconfigdir} *.py
 %{_rpmconfigdir}/pythonbundles.py
 
 %changelog
+* Mon Apr 19 2021 Miro Hrončok <mhroncok@redhat.com> - 12-6
+- Get rid of distutils deprecation warning (by not using it)
+- The distutils module is deprecated in Python 3.10+
+- https://www.python.org/dev/peps/pep-0632/
+
 * Wed Mar 31 2021 Miro Hrončok <mhroncok@redhat.com> - 12-5
 - Do not generate setuptools requirement for console_scripts on Python 3.10+
 - See https://fedoraproject.org/wiki/Changes/Reduce_dependencies_on_python3-setuptools