tests: cleanup test code

- remove unused imports in test cases
- fix code smells and code style in conftest.py

test/test_http2/test_http2_global_disabled.py

@@ -1,6 +1,6 @@
-import pytest
 import re
 
+
 def test_http2_global_disabled_config(docker_compose, nginxproxy):
     conf = nginxproxy.get_conf().decode('ASCII')
     r = nginxproxy.get("http://http2-global-disabled.nginx-proxy.tld")