Enforce the use of a maximum length in paths

When setting a path or creating a link.
Remove the use RadosFsFile::sanitizePath

This implementation is outdated and can be replaced by the base class's.
Use the file path format in the constr/update
test: Remove the check of an exception in CreateFile

The exception is never thrown because now, setting the root as the
file path (just like any other directory path) is allowed.
test: Add new UT for the use of long paths