Ensure sync is complete prior to leaving configmanager sync

The initialization lock is meant to avoid collective and generic
initialization stepping on each other.  This is somewhat reduced in
efficacy if one has a sync running while the other is changing relevant
data.

confluent_server/confluent/config/configmanager.py

@@ -626,7 +626,7 @@ def rollback_clear():
     _cfgstore = _oldcfgstore
     _oldtxcount = 0
     _oldcfgstore = None
-    ConfigManager._bg_sync_to_file()
+    ConfigManager.wait_for_sync(True)
 
 
 def clear_configuration():
@@ -990,6 +990,7 @@ class ConfigManager(object):
             if 'nodes' not in self._cfgstore:
                 self._cfgstore['nodes'] = {}
             self._bg_sync_to_file()
+            self.wait_for_sync()
 
     def get_collective_member(self, name):
         return get_collective_member(name)