modify msg param_keys type to list
Merge remote-tracking branch 'origin/zhaoyang' into v0.2, OK
Add load_status to MFile for load system; DM send rep/del request in standalone thread to increase performance; Allocate new file in table's node group; Optimize findbackupdevice; Create root user automatically; Unit test for file based migration; Implement reopen file; Fix alter_table msg handling.