Ensure lsb-release is present on Debian upgrade tests

Facter 4 has can derive os.distro.codename from /etc/os-release but
Facter 3 needs lsb-release to be present.

It also moves the unsupported_puppetserver definition to use the release
major instead of the codename to avoid needing lsb-release.

spec/acceptance/puppetserver_upgrade_spec.rb

@@ -26,8 +26,12 @@
 
   case fact('osfamily')
   when 'Debian'
-    from_version_exact = "#{from_version}-1#{fact('lsbdistcodename')}"
-    to_version_exact = "#{to_version}-1#{fact('lsbdistcodename')}"
+    if ENV['BEAKER_PUPPET_COLLECTION'] == 'puppet6'
+      # Facter 3 needs lsb-release for the os.distro.codename fact
+      on default, puppet('resource package lsb-release ensure=installed')
+    end
+    from_version_exact = "#{from_version}-1#{fact('os.distro.codename')}"
+    to_version_exact = "#{to_version}-1#{fact('os.distro.codename')}"
   else
     from_version_exact = from_version
     to_version_exact = to_version

spec/support/acceptance/puppetserver.rb

@@ -3,6 +3,6 @@ def unsupported_puppetserver
   when 'Fedora'
     true
   when 'Ubuntu'
-    ENV['BEAKER_PUPPET_COLLECTION'] == 'puppet6' && host_inventory['facter']['os']['distro']['codename'] == 'focal'
+    ENV['BEAKER_PUPPET_COLLECTION'] == 'puppet6' && host_inventory['facter']['os']['release']['major'] == '20.04'
   end
 end