Change JRE repository root

Previously the OpenJDK Repository root was located in the
jres.gopivotal.com S3 bucket.  As we'll need to store other artifacts,
this bucket name was not very good.  This change updates the
repository root to look into the download.pivotal.io S3 bucket.

[#51641279]
Merge 51641279-jre-bucket-name to master

[Completes #51641279]