Fix cv2 import error and some issues for lamb (#41500)

* fix image cv2 import

* fix lamb

python/paddle/dataset/image.py

@@ -54,7 +54,10 @@ if six.PY3:
     if retcode != 0:
         cv2 = None
     else:
+        try:
             import cv2
+        except ImportError:
+            cv2 = None
 else:
     try:
         import cv2

python/paddle/incubate/optimizer/distributed_fused_lamb.py

@@ -17,7 +17,7 @@ from paddle.fluid.framework import Variable
 from paddle.fluid.clip import ClipGradByGlobalNorm
 from paddle.fluid.initializer import Constant
 from paddle.fluid.layer_helper import LayerHelper
-from paddle.optimizer import Optimizer
+from paddle.fluid.optimizer import Optimizer
 from paddle.distributed import get_rank, get_world_size
 from paddle.fluid.executor import global_scope
 from paddle.fluid.framework import name_scope
@@ -42,11 +42,7 @@ class DistributedFusedLamb(Optimizer):
         assert not framework._non_static_mode(
         ), "DistributedFusedLamb does not support dygraph mode"
         super(DistributedFusedLamb, self).__init__(
-            learning_rate=learning_rate,
-            parameters=parameters,
-            weight_decay=None,
-            grad_clip=None,
-            name=name)
+            learning_rate=learning_rate, grad_clip=None, name=name)
 
         self._beta1 = beta1
         self._beta2 = beta2