Packaging: Use a local mirror for the mead repository

The quickstarts build uses a local mirror for the Maven Central repo: https://github.com/infinispan/jdg-packaging/blob/4b47e20056bebd52cda38506690a65284298a21f/release-jdg-7.2.x/maven-settings-quickstarts.xml#L95

We should also use a local mirror for the MEAD repository (as well as Maven Central) in all the packaging Maven settings, because each nightly build will need to download those artifacts. Because most artifacts are very small, latency is a big factor, so a local mirror will help.