Use TLS for downloading artifacts during build

Zookeeper builds are downloading dependencies using the insecure http:// protocol.

An outdated java.net repository can be removed now, since its content is now on maven.org.

The https://repo2.maven.org cannot be used, since its certificate is invalid. Use repo1.maven.org instead (IMHO this is intentional).

Appended you'll find a proposed patch (against git head) to fix these issues, for a starter.