(#13289) Change test scaffolding to use a module & manifest dir fixture path

This removes the need for depending on a global site.pp, and depending on the
checked out apt module to be called 'apt' as well.

It pulls in stdlib via sub-modules as I don't have a better way to deal with
dependencies yet. It has pinned the revision for stdlib to 2.2.1 which is the
minimum required version for apt to work.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "spec/fixtures/modules/stdlib"]
+	path = spec/fixtures/modules/stdlib
+	url = https://github.com/puppetlabs/puppetlabs-stdlib.git

spec/fixtures/modules/apt

@@ -0,0 +1 @@
+../../../

spec/fixtures/modules/stdlib

@@ -0,0 +1 @@
+Subproject commit a70b09d5de035de5254ebe6ad6e1519a6d7cf588

spec/spec_helper.rb

@@ -1,11 +1,14 @@
-require 'puppet'
 require 'rubygems'
+require 'puppet'
 require 'rspec-puppet'
 
 def param_value(subject, type, title, param)
   subject.resource(type, title).send(:parameters)[param.to_sym]
 end
 
+fixture_path = File.expand_path(File.join(File.dirname(__FILE__), 'fixtures'))
+
 RSpec.configure do |c|
-  c.module_path = File.join(File.dirname(__FILE__), '../../')
+  c.module_path = File.join(fixture_path, 'modules')
+  c.manifest_dir = File.join(fixture_path, 'manifests')
 end