Annual cleanup (#2159)

-  Simplify setup.py: remove unneeded features and get rid of deprecation warnings
-  Compatibility with Python 3.10: handle `threading.Event.isSet()` deprecation
-  Make sure setup.py could run without `six`: move Patroni class and main function to the `__main__.py`. The `__init__.py` will have only a few functions used by the Patroni class and from the setup.py

tests/test_patroni.py

@@ -13,7 +13,8 @@ from patroni.dcs.etcd import AbstractEtcdClientWithFailover
 from patroni.exceptions import DCSError
 from patroni.postgresql import Postgresql
 from patroni.postgresql.config import ConfigHandler
-from patroni import Patroni, main as _main, patroni_main, check_psycopg
+from patroni import check_psycopg
+from patroni.__main__ import Patroni, main as _main, patroni_main
 from six.moves import BaseHTTPServer, builtins
 from threading import Thread
 
@@ -97,7 +98,7 @@ class TestPatroni(unittest.TestCase):
 
     @patch('os.getpid')
     @patch('multiprocessing.Process')
-    @patch('patroni.patroni_main', Mock())
+    @patch('patroni.__main__.patroni_main', Mock())
     def test_patroni_main(self, mock_process, mock_getpid):
         mock_getpid.return_value = 2
         _main()

tests/test_raft.py

@@ -157,6 +157,6 @@ class TestRaft(unittest.TestCase):
     @patch('threading.Event')
     def test_init(self, mock_event, mock_kvstore):
         mock_kvstore.return_value.applied_local_log = False
-        mock_event.return_value.isSet.side_effect = [False, True]
+        mock_event.return_value.is_set.side_effect = [False, True]
         self.assertIsNotNone(Raft({'ttl': 30, 'scope': 'test', 'name': 'pg', 'patronictl': True,
                                    'self_addr': '1', 'data_dir': self._TMP}))

tests/test_zookeeper.py

@@ -245,7 +245,7 @@ class TestZooKeeper(unittest.TestCase):
 
     def test_watch(self):
         self.zk.watch(None, 0)
-        self.zk.event.isSet = Mock(return_value=True)
+        self.zk.event.is_set = Mock(return_value=True)
         self.zk._fetch_status = False
         self.zk.watch(None, 0)