Cannot delete full directory structure from Directory in File Share

**Is your feature request related to a problem? Please describe.**

The `az storage file upload-batch` command can be used to upload a full directory structure to an Azure File Share or Directory.

The `az storage file delete-batch` command can be used to recursively delete all the files in an Azure File Share or Directory. It does however leave all the empty subfolders.

There does not seem to be a way of deleting all the empty subfolders - unless each subfolder is deleted individually. This requires prior knowledge of the folder names.

**Describe the solution you'd like**

The `az storage file delete-batch` command should have an option to delete empty subfolders.
Alternatively, or additionally, the `az storage directory delete` should have an option to delete all subfolders.

**Describe alternatives you've considered**

Note that is is possible to delete the whole file share using `az storage share delete --name sparkysfileshare` just not a specific directory within a file share.

**Additional context**

Here's an example workflow:

```
> az storage directory create --name sparkysfolder --share-name sparkysfileshare
{
"created": true
}

> az storage file upload-batch --destination sparkysfileshare --source I:\temp\test --destination-path sparkysfolder --pattern *

uploading I:\temp\test\test1.txt
Finished[#############################################################] 100.0000%
uploading I:\temp\test\subfolder\test2.txt
Finished[#############################################################] 100.0000%
[
"https://vsoftfilestorageac.file.core.windows.net/sparkysfileshare/sparkysfolder/test1.txt",
"https://vsoftfilestorageac.file.core.windows.net/sparkysfileshare/sparkysfolder/subfolder/test2.txt"
]

> az storage file list --share-name sparkysfileshare --path sparkysfolder

[
{
"metadata": null,
"name": "test1.txt",
"properties": {
"contentLength": 4,
"contentRange": null,
"contentSettings": {
"cacheControl": null,
"contentDisposition": null,
"contentEncoding": null,
"contentLanguage": null,
"contentMd5": null,
"contentType": null
},
"copy": {
"completionTime": null,
"id": null,
"progress": null,
"source": null,
"status": null,
"statusDescription": null
},
"etag": null,
"lastModified": null,
"serverEncrypted": null
},
"type": "file"
},
{
"metadata": null,
"name": "subfolder",
"properties": {
"etag": null,
"lastModified": null,
"serverEncrypted": null
},
"type": "dir"
}
]

> az storage file delete-batch --source sparkysfileshare --pattern sparkysfolder\* --account-name vsoftfilestorageac

> az storage file list --share-name sparkysfileshare --path sparkysfolder

[
{
"metadata": null,
"name": "subfolder",
"properties": {
"etag": null,
"lastModified": null,
"serverEncrypted": null
},
"type": "dir"
}
]

> az storage directory delete --name sparkysfolder --share-name sparkysfileshare

The command failed with an unexpected error. Here is the traceback:

The specified directory is not empty. ErrorCode: DirectoryNotEmpty
DirectoryNotEmptyThe specified directory is not empty.
RequestId:17d1cf8b-001a-000b-7fab-f584e4000000
Time:2019-04-18T05:59:17.7350008Z
Traceback (most recent call last):
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\knack\knack\cli.py", line 206, in invoke
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\commands\__init__.py", line 326, in execute
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\commands\__init__.py", line 384, in _run_jobs_serially
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\commands\__init__.py", line 377, in _run_job
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\six\six.py", line 693, in reraise
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\commands\__init__.py", line 354, in _run_job
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\commands\__init__.py", line 145, in __call__
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-cli-core\azure\cli\core\__init__.py", line 451, in default_command_handler
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\file\fileservice.py", line 1035, in delete_directory
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\common\_error.py", line 97, in _dont_fail_not_exist
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\file\fileservice.py", line 1032, in delete_directory
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\common\storageclient.py", line 381, in _perform_request
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\common\storageclient.py", line 306, in _perform_request
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\common\storageclient.py", line 292, in _perform_request
File "C:\Users\VSSADM~1\AppData\Local\Temp\pip-install-z6u9vbmn\azure-multiapi-storage\azure\multiapi\storage\v2018_03_28\common\_error.py", line 115, in _http_error_handler
azure.common.AzureConflictHttpError: The specified directory is not empty. ErrorCode: DirectoryNotEmpty
DirectoryNotEmptyThe specified directory is not empty.
RequestId:17d1cf8b-001a-000b-7fab-f584e4000000
Time:2019-04-18T05:59:17.7350008Z
```