Fix config sync on dead writer

The sync thread can die without clearing syncrunning.  Make sure that
the thread is alive *and* that the thread has not indicated
intent to give up.

confluent_server/confluent/collective/manager.py

@@ -82,7 +82,7 @@ def connect_to_leader(cert=None, name=None, leader=None):
                     log.log({
                         'info': 'Collective initialization in progress on '
                                 '{0}, will retry connection'.format(leader),
-                        'subsystem': 'collective'})
+                        'subsystem': 'collective'}) ####### bad idea?
                     eventlet.spawn_after(random.random(), connect_to_leader,
                                          cert, name, leader)
                     return True

confluent_server/confluent/config/configmanager.py

@@ -2061,7 +2061,8 @@ class ConfigManager(object):
         if statelessmode:
             return
         with cls._syncstate:
-            if cls._syncrunning:
+            if (cls._syncrunning and cls._cfgwriter is not None and
+                    cls._cfgwriter.isAlive()):
                 cls._writepending = True
                 return
             cls._syncrunning = True