Tests: removed TestApplicationTLS.get_server_certificate().

distutils.version is replaced by packaging.version.  Also minor style fixes.

test/test_asgi_lifespan.py

@@ -1,14 +1,16 @@
 import os
-from distutils.version import LooseVersion
 
 from conftest import unit_stop
+from packaging import version
 from unit.applications.lang.python import TestApplicationPython
 from unit.option import option
 
 
 class TestASGILifespan(TestApplicationPython):
     prerequisites = {
-        'modules': {'python': lambda v: LooseVersion(v) >= LooseVersion('3.5')}
+        'modules': {
+            'python': lambda v: version.parse(v) >= version.parse('3.5')
+        }
     }
     load_module = 'asgi'