Fixed bad for loop instruction.

Signed-off-by: Cristiano Urban <cristiano.urban@inaf.it>

transfer_service/tape_client.py

@@ -44,7 +44,7 @@ class TapeClient(object):
         exitCode = stdout.channel.recv_exit_status()
         if not exitCode:
             result = json.loads(stdout.readlines()[0].rstrip('\n'))
-            for el in result:
+            for el in result["payload"]:
                 pool = TapePool()
                 pool.id = el["id"]
                 pool.name = el["name"]