Make BuildFidPath more efficient.
Scan a Lustre tree of any depth.

The scanning is now done from /mount_point/.lustre/fid/ instead of the regular Linux path.
Let rbh-find and rbh-du print any length pathnames.
Fix test 100.
Only pick a default config file if there is only one matching file.
And do not have several directories that can contains config files.

If there is several config files then Robinhood will not use any.
Previously, RH would pick, randomly, the first file it found in a
given set of directories, including the current directory ('.').
This was just a problem waiting to happen.