modulesync 2.5.0 and drop Puppet4 support

[bastelfreak]

Pull Request (PR) description

This Pull Request (PR) fixes the following issues

[ekohl]

The class specs also need to be migrated

[dhollinger]

Looks to be a few things that need cleanup. Will add more as I dig deeper

[ekohl]

A pattern I've started to use instead is:

let(:params) do
  {
    # ...
  }
end

Then when you need to override it below:

let(:params) { super().merge(install_method: 'package') }