update fact_on() from facter to puppet facts

Both tools support json output. For `puppet facts` it's even the
default. `puppet facts` is the successor of `facter`. Newer facts, like
`puppetversion` are not shown by `facter`, but `puppet facts`.

lib/beaker_puppet_helpers/dsl.rb

@@ -205,18 +205,8 @@ def apply_manifest(manifest, opts = {}, &block)
     def fact_on(host, name, opts = {})
       raise(ArgumentError, "fact_on's `name` option must be a String. You provided a #{name.class}: '#{name}'") unless name.is_a?(String)
 
-      if opts.is_a?(Hash)
-        opts['json'] = nil
-      else
-        opts << ' --json'
-      end
-
-      result = on host, Beaker::Command.new('facter', [name], opts)
-      if result.is_a?(Array)
-        result.map { |res| JSON.parse(res.stdout)[name] }
-      else
-        JSON.parse(result.stdout)[name]
-      end
+      result = on host, Beaker::Command.new('puppet', 'facts', 'show', [name], opts)
+      JSON.parse(result.stdout)[name]
     end
 
     # Get a facter fact from the default host