PoC: Patroni on pure RAFT (#375)

* new node can join the cluster dynamically and become a part of consensus
 * it is also possible to join only Patroni cluster (without adding the node to the raft), just comment or remove `raft.self_addr` for that
 * when the node joins the cluster it is using values from `raft.partner_addrs` only for initial discovery.
* It is possible to run Patroni and Postgres on two nodes plus one node with `patroni_raft_controller` (without Patroni and Postgres). In such setup one can temporarily lose one node without affecting the primary.

tests/test_raft_controller.py

@@ -0,0 +1,46 @@
+import logging
+import os
+import unittest
+
+from mock import Mock, patch
+from pysyncobj import SyncObj
+from patroni.config import Config
+from patroni.raft_controller import RaftController, main as _main
+
+from . import SleepException
+
+
+class TestPatroniRaftController(unittest.TestCase):
+
+    SELF_ADDR = '127.0.0.1:5360'
+
+    def remove_files(self):
+        for f in ('journal', 'dump'):
+            f = self.SELF_ADDR + '.' + f
+            if os.path.exists(f):
+                os.unlink(f)
+
+    @patch('pysyncobj.tcp_server.TcpServer.bind', Mock())
+    def setUp(self):
+        self._handlers = logging.getLogger().handlers[:]
+        self.remove_files()
+        os.environ['PATRONI_RAFT_SELF_ADDR'] = self.SELF_ADDR
+        config = Config('postgres0.yml', validator=None)
+        self.rc = RaftController(config)
+
+    def tearDown(self):
+        logging.getLogger().handlers[:] = self._handlers
+        self.remove_files()
+
+    def test_reload_config(self):
+        self.rc.reload_config()
+
+    @patch('logging.Logger.error', Mock(side_effect=SleepException))
+    @patch.object(SyncObj, 'doTick', Mock(side_effect=Exception))
+    def test_run(self):
+        self.assertRaises(SleepException, self.rc.run)
+        self.rc.shutdown()
+
+    @patch('sys.argv', ['patroni'])
+    def test_patroni_raft_controller_main(self):
+        self.assertRaises(SystemExit, _main)