Add 'address' and 'backing_dir' to mfs and misc improvements.
Add 'address' and 'backing_dir' to mfs and misc improvements.

- removed extra trace
- When checking for an available port, don't print the exception and only
  return False on a "port not available" error.
- Only use getpass() when stdin is a TTY, otherwise just do a plain read.
- On "delete", don't try to remove the path if it doesn't exist and unmount it
  if it's currently mounted

google/mawfs,google/mawfs,google/mawfs