Prevent failure from race creating fetch directory

Prevent failure from race creating fetch directory

When multiple monitor hosts attempt to create the fetch directory there
is the potential for the task to fail with:

  "OSError: [Errno 17] File exists: 'fetch'"

This appear to be an issue with the file module trying to create the
same directory at the same time when the tasks has been delegated to a
single host.

This commit enables run_once on the affected task which should address
the issue.