Add custom_objects in the function layer_test
Add custom_objects in the function layer_test

layer test for custom layer

Usage:
```
testing_utils.layer_test(
    SyncBatchNormalization,
    # keras.layers.BatchNormalization,
    kwargs={
      'momentum': 0.9,
      'epsilon': 0.1,
      'gamma_regularizer': keras.regularizers.l2(0.01),
      'beta_regularizer': keras.regularizers.l2(0.01)
    },
    input_shape=(3, 4, 2),
    custom_objects={'SyncBatchNormalization': SyncBatchNormalization})
```
Intel-tensorflow/tensorflow,gunan/tensorflow,petewarden/tensorflow,sarvex/tensorflow,freedomtan/tensorflow,frreiss/tensorflow-fred,frreiss/tensorflow-fred,petewarden/tensorflow,freedomtan/tensorflow,sarvex/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,paolodedios/tensorflow,sarvex/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_tf_optimizer,aam-at/tensorflow,aldian/tensorflow,frreiss/tensorflow-fred,annarev/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aldian/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aldian/tensorflow,Intel-tensorflow/tensorflow,Intel-Corporation/tensorflow,paolodedios/tensorflow,yongtang/tensorflow,aldian/tensorflow,sarvex/tensorflow,yongtang/tensorflow,petewarden/tensorflow,frreiss/tensorflow-fred,gunan/tensorflow,paolodedios/tensorflow,annarev/tensorflow,tensorflow/tensorflow-pywrap_saved_model,paolodedios/tensorflow,frreiss/tensorflow-fred,yongtang/tensorflow,gunan/tensorflow,Intel-tensorflow/tensorflow,karllessard/tensorflow,frreiss/tensorflow-fred,cxxgtxy/tensorflow,aldian/tensorflow,aldian/tensorflow,sarvex/tensorflow,cxxgtxy/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-pywrap_saved_model,cxxgtxy/tensorflow,gunan/tensorflow,aam-at/tensorflow,gautam1858/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,petewarden/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,cxxgtxy/tensorflow,davidzchen/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,freedomtan/tensorflow,tensorflow/tensorflow,gunan/tensorflow,davidzchen/tensorflow,gautam1858/tensorflow,davidzchen/tensorflow,aam-at/tensorflow,gunan/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gunan/tensorflow,tensorflow/tensorflow-pywrap_saved_model,annarev/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_saved_model,frreiss/tensorflow-fred,Intel-Corporation/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow,karllessard/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,aam-at/tensorflow,petewarden/tensorflow,davidzchen/tensorflow,frreiss/tensorflow-fred,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,annarev/tensorflow,aldian/tensorflow,sarvex/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,aam-at/tensorflow,aam-at/tensorflow,petewarden/tensorflow,aam-at/tensorflow,annarev/tensorflow,gautam1858/tensorflow,petewarden/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,yongtang/tensorflow,Intel-tensorflow/tensorflow,yongtang/tensorflow,gunan/tensorflow,Intel-Corporation/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_saved_model,freedomtan/tensorflow,petewarden/tensorflow,Intel-tensorflow/tensorflow,Intel-Corporation/tensorflow,aam-at/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,davidzchen/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,freedomtan/tensorflow,davidzchen/tensorflow,davidzchen/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-tensorflow/tensorflow,petewarden/tensorflow,paolodedios/tensorflow,annarev/tensorflow,gunan/tensorflow,tensorflow/tensorflow,petewarden/tensorflow,gunan/tensorflow,Intel-tensorflow/tensorflow,Intel-Corporation/tensorflow,freedomtan/tensorflow,yongtang/tensorflow,annarev/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,aam-at/tensorflow,freedomtan/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-Corporation/tensorflow,yongtang/tensorflow,gunan/tensorflow,karllessard/tensorflow,annarev/tensorflow,annarev/tensorflow,davidzchen/tensorflow,annarev/tensorflow,paolodedios/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,aldian/tensorflow,frreiss/tensorflow-fred,annarev/tensorflow,karllessard/tensorflow,davidzchen/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,yongtang/tensorflow,davidzchen/tensorflow,Intel-tensorflow/tensorflow,aam-at/tensorflow,sarvex/tensorflow,aam-at/tensorflow,tensorflow/tensorflow,aam-at/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-Corporation/tensorflow,tensorflow/tensorflow,davidzchen/tensorflow,Intel-Corporation/tensorflow,gautam1858/tensorflow,freedomtan/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,karllessard/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,yongtang/tensorflow,gunan/tensorflow,cxxgtxy/tensorflow,davidzchen/tensorflow,gautam1858/tensorflow,cxxgtxy/tensorflow,frreiss/tensorflow-fred,petewarden/tensorflow,sarvex/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer