scanFiles no longer throws an exception if the directory doesn't exist (PLAT-567)

Since the common use-case is that we want to check if there are any files
under a path, not check that the path exists, we make the default to not
throw.
Merge pull request #6 from datacratic/PLAT-567-scanFiles-no-exception-on-missing-directory

scanFiles no longer throws an exception if the directory doesn't exist (PLAT-567)