Change the order of package build

We currently build all packages when tagging a release. We still need to do that but we can have the package required for deployments done first.

This requires a change in the omnibus-gitlab release pipelines:

1. On tag, move Ubuntu 16.04 build as the first step in the pipeline
2. Inside of the same job, build the package AND upload it to a private package repository
3. Create a way to poll the package server for the availability of the package

The poll part can be done in a few ways, but ideally this should not be done inside of the omnibus-gitlab pipeline.

cc @gitlab-org/delivery