Fix node group modification of node parameters

Commit 904b3bfe tried to fix the deletion of custom ndparams from
group, but instead broke both modification and deletion: because we
run ForceDictType on self.op.ndparams instead of the updated
new_ndparams, we can neither delete nor set properly spindle_count
(since it won't be coerced to int).

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

lib/cmdlib.py

@@ -13966,7 +13966,7 @@ class LUGroupSetParams(LogicalUnit):
     if self.op.ndparams:
       new_ndparams = _GetUpdatedParams(self.group.ndparams, self.op.ndparams)
-      utils.ForceDictType(self.op.ndparams, constants.NDS_PARAMETER_TYPES)
+      utils.ForceDictType(new_ndparams, constants.NDS_PARAMETER_TYPES)
       self.new_ndparams = new_ndparams
     if self.op.diskparams: