Broker list not randomized

[gunnartangring]

Describe the bug
By design KafkaJS should randomize with of the brokers listed it bootstraps to but in reality this does not happen.

To Reproduce

1. Unit testing of https://github.com/tulios/kafkajs/blob/master/src/cluster/connectionPoolBuilder.js#L93 with multiple brokers defined

Expected behavior
A random broker will be returned

Observed behavior
The first broker will be returned deterministically

Environment:
(All)

Additional context
A fix was added in v 1.12 randomizing the order of bootstrap brokers, but this fix was later reverted in v 1.13.
#631