Don't demote master if failed to update leader key in pause (#668)

Fixes https://github.com/zalando/patroni/issues/659

patroni/ha.py

@@ -771,6 +771,8 @@ class Ha(object):
                 # Either there is no connection to DCS or someone else acquired the lock
                 logger.error('failed to update leader lock')
                 if self.state_handler.is_leader():
+                    if self.is_paused():
+                        return 'continue to run as master after failing to update leader lock in DCS'
                     self.demote('immediate-nolock')
                     return 'demoted self because failed to update leader lock in DCS'
                 else:

tests/test_ha.py

@@ -623,6 +623,14 @@ class TestHa(unittest.TestCase):
         self.ha.cluster = get_cluster_initialized_with_leader(Failover(0, '', self.p.name, None))
         self.assertEquals(self.ha.run_cycle(), 'PAUSE: waiting to become master after promote...')
 
+    def test_failed_to_update_lock_in_pause(self):
+        self.ha.update_lock = false
+        self.ha.is_paused = true
+        self.p.name = 'leader'
+        self.ha.cluster = get_cluster_initialized_with_leader()
+        self.assertEquals(self.ha.run_cycle(),
+                          'PAUSE: continue to run as master after failing to update leader lock in DCS')
+
     def test_postgres_unhealthy_in_pause(self):
         self.ha.is_paused = true
         self.p.is_healthy = false