[3.1][worker] Fixes problem with repr(Worker) when blueprint not yet set. Closes #2514

celery/worker/__init__.py

@@ -326,7 +326,9 @@ class WorkController(object):
 
     def __repr__(self):
         return '<Worker: {self.hostname} ({state})>'.format(
-            self=self, state=self.blueprint.human_state(),
+            self=self,
+            state=(self.blueprint.human_state()
+                   if self.blueprint else 'initializing'),  # Issue #2514
         )
 
     def __str__(self):