Replacing with public docker image for pretraining

Author: aashnamsft

pretrain/PyTorch/notebooks/BERT_Pretrain.ipynb

@@ -264,12 +264,8 @@
     "# Define the project folder\n",
     "project_folder = '..' # This is to allow the libraries stored under pytorch/ to be loaded\n",
     "\n",
-    "## !!!! update the following values before proceeding !!!!\n",
-    "image_name = '<image name goes here>'\n",
-    "image_registry_details = ContainerRegistry()\n",
-    "image_registry_details.address = \"<acr name goe shere>.azurecr.io\"\n",
-    "image_registry_details.username = \"<acr user name goes here>\"\n",
-    "image_registry_details.password = \"<acr user password goes here>\"\n",
+    "## Using a public image published on Azure.\n",
+    "image_name = 'mcr.microsoft.com/azureml/bert:pretrain-openmpi3.1.2-cuda10.0-cudnn7-ubuntu16.04'\n",
     "\n",
     "# Using MPI to execute a distributed run\n",
     "mpi = MpiConfiguration()\n",
@@ -289,7 +285,6 @@
     "                    #Docker image\n",
     "                    use_docker=True,\n",
     "                    custom_docker_image=image_name,\n",
-    "                    image_registry_details=image_registry_details,\n",
     "                    user_managed=True,\n",
     "                    \n",
     "                    # Training script parameters\n",