Default bztar format for sdist command

Usage of the 'bztar' format is unchanged, just changing the way
of configuration. The previous method was deprecated.

Signed-off-by: Ondrej Nosek <onosek@redhat.com>
(cherry picked from commit 88327d5784)

MANIFEST.in

@@ -2,6 +2,7 @@ include AUTHORS
 include COPYING
 include GPL
 include pungi.spec
+include setup.cfg
 include tox.ini
 include share/*
 include share/multilib/*

setup.cfg

@@ -0,0 +1,2 @@
+[sdist]
+formats=bztar

setup.py

@@ -5,14 +5,9 @@
 import os
 import glob
 
-import distutils.command.sdist
 from setuptools import setup
 
 
-# override default tarball format with bzip2
-distutils.command.sdist.sdist.default_format = {"posix": "bztar"}
-
-
 # recursively scan for python modules to be included
 package_root_dirs = ["pungi", "pungi_utils"]
 packages = set()