Move safeFileName from source/http to source/util/pathutil
and apply it to the containerblob source as well. Harden
containerblob/pull.go to use os.OpenRoot for file writes,
preventing path traversal via crafted filenames.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
(cherry picked from commit 3d6e587655d72c343f6fdc7268480a900ba45b0c)
