public void append(final StringBuilder sb) {
            final long age = System.currentTimeMillis() - refreshTime;

            clusterLockKey.append(sb);
            sb.append(" age=");
            sb.append(ModelStringUtil.formatDurationString(age));
        }
Every 10 minutes try and unlock/remove any locks that we hold that have
not been refreshed by their owner for 10 minutes.
stroom-cluster/stroom-cluster-lock-impl-db/src/main/java/stroom/cluster/lock/impl/db/ClusterLockClusterHandler.java