Created by: wangchaochaohu

Add python unitest for fusion groups base on https://github.com/PaddlePaddle/Paddle/pull/22209, It validates the correctness for python api. Python端: elementwise_add + elementwise_mul 融合 匹配一个子图

c = pre_cell * layers.sigmoid(f) + layers.sigmoid( i) * layers.tanh(j) m = layers.tanh(c) * layers.sigmoid(o) 匹配成1个子图

d = (a-b) * c e = relu(d) f = relu(sigmoid(g)) h = mul(e, f) 匹配两个子图