(maint) Use puppet6 release repos for PuppetDB
(maint) Use puppet6 release repos for PuppetDB

Now that the changes we need for Hiera lookup data collection have been
released in PDB, this commit updates our tests to use the puppet6
release repos, which will pull in the latest released version of PDB in
that stream.

puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppet-server,puppetlabs/puppetserver