naming: change taskStopChan to NodeProducer
add dummyMaster testablyFail
add controller failure detection
use standby in node_failure_test
finish test slave ParentDataReady fail
fix WaitFailure
fix race in setepoch; waitFailure should take 'set' cmd
fix a race that dataReqStop is nil when receiving req
style fix
random select any failed task
logging improvement
Merge pull request #95 from fengjingchao/master

failover option & standby