Enable snap expiry even if no new snaps

If autosnap does not identify that any snaps need creating it terminates preventing stale snapshots from being expired and replication from running.  This will also fix #2345

This change lets autosnap - create, expire and run replication regardless of snapshot creation.  

An alternative solution would be to split autosnap into create and expire scripts and then have three cron jobs running createsnap, expiresnap and replicate scripts.  If this is preferred approach please advise and I will look to code