(Maint) Update stubbing to work with facter 1.7.4

Facter 1.7.4 changed how it decides on what directory to look in for
facts.d based on the user it is running as. This stubs out that bit of
code to make it think it is running as root.

spec/unit/facter/pe_required_facts_spec.rb

@@ -9,6 +9,7 @@ describe "External facts in /etc/puppetlabs/facter/facts.d/puppet_enterprise_ins
   context "With Facter 1.6.17 which does not have external facts support" do
     before :each do
       Facter.stubs(:version).returns("1.6.17")
+      Facter::Util::Root.stubs(:root?).returns(true)
       # Stub out the filesystem for stdlib
       Dir.stubs(:entries).with("/etc/puppetlabs/facter/facts.d").
         returns(['puppet_enterprise_installer.txt'])