Use /var/lib/ntp/drift/ntp.drift on SUSE

Signed-off-by: Tim Serong <tserong@suse.com>
(cherry picked from commit 0f6c968c243d0b4baa55c4fa192fcc50f10d3e2e)
Merge pull request #28 from vuntz/release/pebbles/master

Use /var/lib/ntp/drift/ntp.drift on SUSE