archive: allow access only to the user

Change mode permission bits to 600

Change-Id: I90a69f1ea9d09915d04bd84339d64ec6d9e6c05a
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
(cherry picked from commit 77d69d24c46207a16ecb5fc732cc1c84de0ca947)