SPARK-1254. Supplemental fix for HTTPS on Maven Central

It seems that HTTPS does not necessarily work on Maven Central, as it does not today at least. Back to HTTP. Both builds works from a clean repo.

Author: Sean Owen <sowen@cloudera.com>

Closes #209 from srowen/SPARK-1254Fix and squashes the following commits:

bb7be47 [Sean Owen] Revert to HTTP for Maven Central repo, as it seems HTTPS does not necessarily work