Log directory path for exceptions

Improve the log message of setup_file_sftp_userdir to include the path that
has been attempted to create.

gvafile/fileservertasks/tasks.py

@@ -100,7 +100,8 @@ def setup_file_sftp_userdir(username, *args, **kwargs):
             sftp_directory], stderr=subprocess.STDOUT)
     except subprocess.CalledProcessError as cpe:
         log_and_raise(
-            cpe, 'could not create SFTP directory for user %s', username)
+            cpe, 'could not create SFTP directory %s for user %s',
+            sftp_directory, username)
     _LOGGER.info(
         'created sftp directory %s for user %s', sftp_directory, username)
     return {'username': username, 'sftp_directory': sftp_directory}