Fix pos_file location

Change-Id: Ifa2787d76cf18e29f54583046349c071c5e9a25e

linux/meta/fluentd.yml

@@ -6,7 +6,7 @@ config:
           type: systemd
           tag: systemd.source
           path: /run/log/journal
-          pos_file: /tmp/fluentd-systemd.pos
+          pos_file: /var/log/td-agent/tmp/systemd.source.pos
           entry:
             field_map:
               MESSAGE: 'Payload'