Rather than push to the gpdb5 bucket prefix, push release candidates for
5.10.X to a dedicated 5.10.X prefix.
Co-authored-by: NJason Vigil <jvigil@pivotal.io>
Co-authored-by: NKris Macoskey <kmacoskey@pivotal.io>
Co-authored-by: NEd Espino <edespino@pivotal.io>