tests/raftstore: refact call_command_on_leader (#498)
tests/raftstore: refact call_command_on_leader (#498)

auto retry if response has error and the error is caused
by leader change
c4pt0r/tikv,BusyJay/tikv,BusyJay/tikv,BusyJay/tikv,BusyJay/tikv,pingcap/tikv,pingcap/tikv