raft/log_test: fixed wrong index
raft/log_test: fixed wrong index

mqliang/etcd,cockroachdb/etcd,ajityagaty/etcd,gyuho/etcd,coreos/etcd,mkumatag/etcd,mkumatag/etcd,li-ang/etcd,rnaveiras/etcd,etcd-io/etcd,rnaveiras/etcd,dannysauer/etcd,dannysauer/etcd,ajityagaty/etcd,li-ang/etcd,gyuho/etcd,coreos/etcd,rnaveiras/etcd,mqliang/etcd,ajityagaty/etcd,etcd-io/etcd,cockroachdb/etcd,mkumatag/etcd,etcd-io/etcd,mqliang/etcd