Reset rewind state if postgres started after successful pg_rewind (#1408)

Close https://github.com/zalando/patroni/issues/1406

patroni/ha.py

@@ -1149,6 +1149,8 @@ class Ha(object):
                 return 'removed leader key after trying and failing to start postgres'
             return 'failed to start postgres'
         self._crash_recovery_executed = False
+        if self._rewind.executed and not self._rewind.failed:
+            self._rewind.reset_state()
         return None
 
     def cancel_initialization(self):

tests/test_ha.py

@@ -618,6 +618,8 @@ class TestHa(PostgresInit):
         member = Member(0, 'test', 1, {'api_url': 'http://localhost:8011/patroni'})
         self.ha.fetch_node_status(member)
 
+    @patch.object(Rewind, 'pg_rewind', true)
+    @patch.object(Rewind, 'check_leader_is_not_in_recovery', true)
     def test_post_recover(self):
         self.p.is_running = false
         self.ha.has_lock = true
@@ -625,6 +627,8 @@ class TestHa(PostgresInit):
         self.assertEqual(self.ha.post_recover(), 'removed leader key after trying and failing to start postgres')
         self.ha.has_lock = false
         self.assertEqual(self.ha.post_recover(), 'failed to start postgres')
+        leader = Leader(0, 0, Member(0, 'l', 2, {"version": "1.6", "conn_url": "postgres://a", "role": "master"}))
+        self.ha._rewind.execute(leader)
         self.p.is_running = true
         self.assertIsNone(self.ha.post_recover())