Further work on permanent physical slots (#2891)

- Fixed issues with has_permanent_slots() method. It didn't took into account the case of permanent physical slots for members, falsely concluding that there are no permanent slots.
- Write to the status key only LSNs for permanent slots (not just for slots that exist on the primary).
  - Include pg_current_wal_flush_lsn() to slots feedback, so that slots on standby nodes could be advanced
- Improved behave tests:
  - Verify that permanent slots are properly created on standby nodes
  - Verify that permanent slots are properly advanced, including DCS failsafe mode
  - Verify that only permanent slots are written to the `/status`

features/steps/basic_replication.py

@@ -110,7 +110,7 @@ def replication_works(context, primary, replica, time_limit):
     context.execute_steps(u"""
         When I add the table test_{0} to {1}
         Then table test_{0} is present on {2} after {3} seconds
-    """.format(int(time()), primary, replica, time_limit))
+    """.format(str(time()).replace('.', '_').replace(',', '_'), primary, replica, time_limit))
 
 
 @then('there is a "{message}" {level:w} in the {node} patroni log')