Fix LUInstanceRecreateDisks with iallocator

Recent iallocator changes (commit fb60bc6a, “iallocator: Add node
whitelist”) broke the parameter validation for LUInstanceRecreateDisks
(the other LUs were manually fixed already):

  $ gnt-instance recreate-disks -I hail --dry-run instance3
  Failure: prerequisites not met for this operation:
  error type: wrong_input, error details:
  Request is missing 'node_whitelist' parameter

By just defining the new parameter, the LU works normally (“INFO:
Selected nodes for instance instance3 via iallocator hail: node2”).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

lib/cmdlib.py

@@ -7540,7 +7540,8 @@ class LUInstanceRecreateDisks(LogicalUnit):
                                         disks=[{constants.IDISK_SIZE: d.size,
                                                 constants.IDISK_MODE: d.mode}
                                                 for d in self.instance.disks],
-                                        hypervisor=self.instance.hypervisor)
+                                        hypervisor=self.instance.hypervisor,
+                                        node_whitelist=None)
     ial = iallocator.IAllocator(self.cfg, self.rpc, req)
     ial.Run(self.op.iallocator)