Use Mirror site instead of Apache.org

Apache.org requests that people NOT download from their site, and to use a mirror instead.  Since we install from their site for every CI build for every project that uses Cassandra, as well as every time someone provisions their local boxes, we hit the repo frequently.  The apache.org repo recently started giving us "403 - Forbidden", causing provisioning to fail.  We should switch to a mirror for now, but consider hosting this privately.