Add Puppet 8 support

[bastelfreak]

also contains #883

[ekohl]

Requires #888

[ekohl]

Please rebase

[ekohl]

Our upgrade test requires versions to be set:

puppet-puppet/spec/acceptance/puppetserver_upgrade_spec.rb

Lines 17 to 23 in 012b369

	case ENV['BEAKER_PUPPET_COLLECTION']
	when 'puppet7'
	from_version = '7.6.0'
	to_version = '7.13.0'
	else
	raise 'Unsupported Puppet collection'
	end

We pick the oldest and newest versions that are available for all the platforms.

[ekohl]

I took the liberty of adding to your PR, hopefully to move things forward.