1. ix bugs in query layer.
2. remove some redundant code in BE
3. support specify multi helper node when starting FE
4. add proc 'cluster_load_statistic' to show load balance situation of Palo
Add new features:
1. plugins of Ambari and k8s deploy
2. specified config 'priority_network' to solve some ip problems
Fix bugs:
fix bugs that rebalance does not work in some case.
fix count(*) from union stmt bug
fix some union stmt bugs
fix bugs when try to schema change a clone replica
