fix: _set_keyspace_for_all_pools passes only the last pool's errors to callback

The pool_finished_setting_keyspace closure was calling callback(host_errors)
instead of callback(errors), so when the last pool to finish had no errors,
the callback received an empty list instead of the accumulated error dict
from all pools.

This caused _set_keyspace_completed to report success (not [] is True)
even when other pools had failures — keyspace changes silently succeeded
with partial failures dropped.

Introduced in d281b50 (2013-10-11).

Fixes #914

Author: mykaul

cassandra/cluster.py

@@ -3438,7 +3438,7 @@ def pool_finished_setting_keyspace(pool, host_errors):
                 errors[pool.host] = host_errors
 
             if not remaining_callbacks:
-                callback(host_errors)
+                callback(errors)
 
         for pool in tuple(self._pools.values()):
             pool._set_keyspace_for_all_conns(keyspace, pool_finished_setting_keyspace)