Renamed --libstatedir to --statedir.

In BSD systems, it's usually </var/db> or some other dir under </var>
that is not </var/lib>, so $statedir is a more generic name.  See
hier(7).

Reported-by: Andrei Zeliankou <zelenkov@nginx.com>
Reported-by: Zhidao Hong <z.hong@f5.com>
Reviewed-by: Konstantin Pavlov <thresh@nginx.com>
Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Cc: Liam Crilly <liam@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

test/conftest.py

@@ -373,7 +373,7 @@ def unit_run(state_dir=None):
         '--no-daemon',
         '--modulesdir',
         build_dir,
-        '--libstatedir',
+        '--statedir',
         state,
         '--pid',
         f'{temp_dir}/unit.pid',