Fix 'start failed' issue (#1262)

The start of postgres happens in two stages:
1. First Patroni is waiting for postgres port to be open
2. After that, it is waiting for postgres starts to accept connections

There is a default timeout 60 seconds for both stages (in total).

When the port isn't open, pg_isready exits with code=2.
If postgres is rejecting connections due to recovery, exit code=1.

In most cases postgres quickly opens the port and pg_isready starts returning 1, but in rare cases the whole timeout could spend in `1.`
After that, the HA loop is still waiting for postgres to start, but executing only the check from `2.`. Since pg_isready exit code is still = 2, Patroni was falsely assuming that 'start failed' without taking into consideration the fact that the postmaster process is up and running.

Fixes https://github.com/zalando/patroni/issues/1160

patroni/postgresql/__init__.py

@@ -561,10 +561,12 @@ class Postgresql(object):
         if ready == STATE_REJECT:
             return False
         elif ready == STATE_NO_RESPONSE:
-            self.set_state('start failed')
-            self.slots_handler.schedule(False)  # TODO: can remove this?
-            self.config.save_configuration_files(True)  # TODO: maybe remove this?
-            return True
+            ret = not self.is_running()
+            if ret:
+                self.set_state('start failed')
+                self.slots_handler.schedule(False)  # TODO: can remove this?
+                self.config.save_configuration_files(True)  # TODO: maybe remove this?
+            return ret
         else:
             if ready != STATE_RUNNING:
                 # Bad configuration or unexpected OS error. No idea of PostgreSQL status.