Update is_a acceptance tests to only run on puppet4

spec/acceptance/is_a_spec.rb

@@ -1,7 +1,8 @@
 #! /usr/bin/env ruby -S rspec
 require 'spec_helper_acceptance'
 
-describe 'is_a function', :unless => UNSUPPORTED_PLATFORMS.include?(fact('operatingsystem')) do
+if get_puppet_version =~ /^4/
+  describe 'is_a function', :unless => UNSUPPORTED_PLATFORMS.include?(fact('operatingsystem')) do
     it 'should match a string' do
       pp = <<-EOS
       if 'hello world'.is_a(String) {
@@ -25,4 +26,5 @@ describe 'is_a function', :unless => UNSUPPORTED_PLATFORMS.include?(fact('operat
         expect(r.stdout).not_to match(/Notice: output wrong/)
       end
     end
+  end
 end

spec/spec_helper_acceptance.rb

@@ -33,9 +33,13 @@ def is_future_parser_enabled?
   return false
 end
 
+def get_puppet_version
+  (on default, puppet('--version')).output.chomp
+end
+
 RSpec.shared_context "with faked facts" do
   let(:facts_d) do
-    puppet_version = (on default, puppet('--version')).output.chomp
+    puppet_version = get_puppet_version
     if fact('osfamily') =~ /windows/i
       if fact('kernelmajversion').to_f < 6.0
         'C:/Documents and Settings/All Users/Application Data/PuppetLabs/facter/facts.d'