Declare puppetserver unsupported on Archlinux

There are no packages so this fails. Previously the acceptance tests
didn't run.

Author: ekohl

spec/support/acceptance/puppetserver.rb

@@ -1,5 +1,7 @@
 def unsupported_puppetserver
   case host_inventory['facter']['os']['name']
+  when 'Archlinux'
+    true
   when 'Fedora'
     true
   when 'Ubuntu'