Ensures a UserPool Id starts like {region}_

moto/cognitoidp/models.py

@@ -24,7 +24,7 @@ class CognitoIdpUserPool(BaseModel):
 
     def __init__(self, region, name, extended_config):
         self.region = region
-        self.id = str(uuid.uuid4())
+        self.id = "{}_{}".format(self.region, str(uuid.uuid4().hex))
         self.name = name
         self.status = None
         self.extended_config = extended_config or {}