There're many 'invalid/unused' members inside a group, so use  all group members count to do cid % operation will filter most files out.
Also it will increase the probability during the probabilityFilter.
So enhance the code to filter out invalid group members

After we change to use batch mode, the time cost to retrieve all work reports from chain
has been reduced from ~100 minutes to ~5 minutes, so we can shorten the updateInterval
update group info every 30 minutes