Restart former master in readonly only once when partitioned (#370)

patroni/ha.py

@@ -636,8 +636,11 @@ class Ha(object):
             else:
                 # Either there is no connection to DCS or someone else acquired the lock
                 logger.error('failed to update leader lock')
-                self.demote('offline')
-                return 'demoted self because failed to update leader lock in DCS'
+                if self.state_handler.is_leader():
+                    self.demote('offline')
+                    return 'demoted self because failed to update leader lock in DCS'
+                else:
+                    return 'not promoting because failed to update leader lock in DCS'
         else:
             logger.info('does not have lock')
         return self.follow('demoting self because i do not have the lock and i was a leader',

tests/test_ha.py

@@ -243,6 +243,8 @@ class TestHa(unittest.TestCase):
         self.ha.has_lock = true
         self.ha.update_lock = false
         self.assertEquals(self.ha.run_cycle(), 'demoted self because failed to update leader lock in DCS')
+        self.p.is_leader = false
+        self.assertEquals(self.ha.run_cycle(), 'not promoting because failed to update leader lock in DCS')
 
     def test_follow(self):
         self.ha.cluster.is_unlocked = false