add DFL support for client.
del_sfilelocation will delete SFL by metastore, so we do not delete it.
Add multithread support for REP/DEL; add sysinfo collection and report to dservice.
Add dflf to MetaStoreClient (not tested yet); change descendingKeySet to default asc order keySet.
Fix zero-byte recv from server bug; Update system info every 60 seconds; catch SIGTERM signal;
Catch Exception in getMP; add FLSelector funcs; add -ofdp;