Created by: typhoonzero

When piecewise_decay is defined the pserver side program will have a wrong conditional_block refer to a block id that doesn't exist on the pserver program.

This error was first met by @kolinwei

optimizer = fluid.optimizer.Momentum(
            learning_rate=fluid.layers.piecewise_decay(
                boundaries=bd, values=lr),
            momentum=0.9,
            regularization=fluid.regularizer.L2Decay(1e-4))