start-shard.sh depends on a private s3 bucket

[guillaug]

start-shard.sh tries to download zookeeper-3.4.3 and kafka-0.7.5 from a private s3 repo.

Zookeeper-3.4.3 can be obtained on the apache project website
Kafka-0.7.5 zip file seems problematic as explained here : 0.7.5 is not an official release