File based persisters should store all files under same folder.

This patch allows each file persister to remove all cached files
as previously but also removes the parent cache folder in order
to allow cleaning all the remaining cached content from lazy/older
persiters which did not clear their content.

This patch also sanitizes not sanitized cache keys.

Signed-off-by: David Marques <dpsmarques@gmail.com>

<!---
@huboard:{"order":76.0}
-->