in case of lookup failure, the benchmark should fail

[filipecosta90]

IPs []
Total clients: 50. Commands per client: 10000 Total commands: 500000
Using random seed: 12345
panic: invalid argument to Int63n

goroutine 1 [running]:
math/rand.(*Rand).Int63n(0x1049a9f80?, 0x7a120?)
	/usr/local/go/src/math/rand/rand.go:110 +0xec
math/rand.Int63n(...)
	/usr/local/go/src/math/rand/rand.go:327
main.main()
	/github/workspace/redis-bechmark-go.go:198 +0x960