We only want to use an old version for glibc which the centos:7
image takes care of.

The old version of git used in debian:8 was causing problems
with the uid/gid passthrough with no user in passwd.

- Instead we now use CentOS 7 for the static build to guarantee
  that we only depend on libc v2.17

- For macOS we now pull in a static node binary and bundle that instead.

Closes #1665

Closes #1656

- Splits up test into fmt, lint and test
- Fixes bug in build-packages.sh
- Minor README.md fixes

Much better test now as well.

The architecture specific jobs pull it in and then build releases.

Much faster!