Fix - Unpublish idempotency and recursive remove_dir

*makes Unpublish idempotent by not failing if the target_path does not exists
*changed remove_dir to be non-recursive and the call will fail if there are any files / sub-directories under the path.

Change-Id: I286d27576b81901e0a57566e591686ffa5649c8b
Signed-off-by: Gil <gvitzinger@nvidia.com>

driver/filesystem_manager.py

@@ -1,5 +1,5 @@
 import logging
-import shutil
+import os
 
 from grpc import StatusCode
 
@@ -126,7 +126,7 @@ def get_fs_type(target_path):
 
 	@staticmethod
 	def remove_dir(dir_path):
-		return shutil.rmtree(dir_path)
+		return os.rmdir(dir_path)
 
 	@staticmethod
 	def format_block_device(block_device_path, fs_type, mkfs_options_str):