#1013 The getHostCandidates method improves
#1017 Increase the catch exception code
#1021 Use a more elegant way to judge empty
#1022 Set up xstream security framework
#1023 Avoid scheduling when DiscoveryClient.shutdown called (fix for #973)
#1026 Get dataCenterInfo when need it && fix typo
#1029 Verify if scheduler is active before submit new task
#1031 prevent replication flood caused by socket read time out leads to some node CPU 100%
#1033 fix potential NPE for issue #1014