Depricate metadata_request_timeout

`metadata_request_timeout` was added to Cluster by mistake, there is already another
option that controls system query timeout - `control_connection_timeout`.
Mark it as depricated, to be removed in next minor release.

Author: dkropachev

cassandra/cluster.py

@@ -1082,6 +1082,8 @@ def default_retry_policy(self, policy):
 
     metadata_request_timeout = datetime.timedelta(seconds=2)
     """
+    Deprecated: use control_connection_timeout instead.
+
     Timeout for all queries used by driver it self.
     Supported only by Scylla clusters.
     """
@@ -1300,6 +1302,7 @@ def __init__(self,
 
         self.auth_provider = auth_provider
         if metadata_request_timeout is not None:
+            warn("metadata_request_timeout is deprecated: use control_connection_timeout instead", DeprecationWarning)
             self.metadata_request_timeout = metadata_request_timeout
 
         if load_balancing_policy is not None: