The distributed version loss doesn't go down.

[gongweibao]

The distributed version fluid's loss doesn't go down.

Pass = 0, Iters = 1, Loss = 4.624973, Accuracy = 0.000000, Speed = 1.84 img/s
Pass = 0, Iters = 2, Loss = 4.624973, Accuracy = 0.000000, Speed = 4.30 img/s
Pass = 0, Iters = 3, Loss = 4.624973, Accuracy = 0.000000, Speed = 4.25 img/s
Pass = 0, Iters = 4, Loss = 4.624973, Accuracy = 0.000000, Speed = 5.06 img/s
Pass = 0, Iters = 5, Loss = 4.624973, Accuracy = 0.000000, Speed = 4.81 img/s
Pass = 0, Iters = 6, Loss = 4.624973, Accuracy = 0.000000, Speed = 5.13 img/s
Pass = 0, Iters = 7, Loss = 4.624973, Accuracy = 0.000000, Speed = 4.40 img/s
Pass = 0, Iters = 8, Loss = 4.624973, Accuracy = 0.000000, Speed = 4.14 img/s

We need unit test to guarantee it.