`az ml folder attach` uses the AML SDK from the environment

- If the issue is to do with Azure CLI 2.0 in-particular, create an issue here at [Azure/azure-cli](https://github.com/Azure/azure-cli/issues)

### Extension name (the extension in question)

ml

### Description of issue (in as much detail as possible)
`az ml folder attach` uses the AML SDK from the environment rather than the one bundled in the extension.

This can be demonstrating by blocking the .azureml folder by writing a file with that name, causing an exception to be raised by the command, which shows the script paths.

```
touch .azureml
az ml folder attach -w ws -g rg

ProjectSystemException:
Message: Traceback (most recent call last):
File "/Users/digdug/.pyenv/versions/3.7.6/envs/my-azureml/lib/python3.7/site-packages/azureml/_project/project_engine.py", line 51, in attach_project
project_manager.attach_project(project_id, project_path, project_arm_scope, compute_target_dict)
File "/Users/digdug/.pyenv/versions/3.7.6/envs/my-azureml/lib/python3.7/site-packages/azureml/_project/project_manager.py", line 104, in attach_project
_base_project_contents_folder_name)
File "/Users/digdug/.pyenv/versions/3.7.6/envs/my-azureml/lib/python3.7/site-packages/azureml/_project/project_manager.py", line 144, in _copy_default_files
shutil.copy(orig_path, new_path)
File "/Users/digdug/.pyenv/versions/3.7.6/lib/python3.7/shutil.py", line 248, in copy
copyfile(src, dst, follow_symlinks=follow_symlinks)
File "/Users/digdug/.pyenv/versions/3.7.6/lib/python3.7/shutil.py", line 121, in copyfile
with open(dst, 'wb') as fdst:
NotADirectoryError: [Errno 20] Not a directory: '/Users/digdug/sample/.azureml/conda_dependencies.yml'
```

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