Fix greenlet 'isAlive'

There is no 'isAlive' in a greenlet.

confluent_server/confluent/collective/manager.py

@@ -403,7 +403,7 @@ def handle_connection(connection, cert, request, local=False):
             connection.close()
             return
         if (currentleader == connection.getpeername()[0] and
-                follower and follower.isAlive()):
+                follower and not follower.dead:
             # if we are happily following this leader already, don't stir
             # the pot
             tlvdata.send(connection, {'status': 0})

confluent_server/confluent/config/configmanager.py

@@ -2338,7 +2338,7 @@ class ConfigManager(object):
             return
         with cls._syncstate:
             if (cls._syncrunning and cls._cfgwriter is not None and
-                    cls._cfgwriter.isAlive()):
+                    not cls._cfgwriter.dead):
                 cls._writepending = True
                 return
             if cls._syncrunning:  # This suggests an unclean write attempt,