create rspec environment for build tests

Rakefile

@@ -1,5 +1,15 @@
+require "bundler"
+begin
+  Bundler.setup(:default, :development)
+rescue Bundler::BundlerError => e
+  raise LoadError.new("Unable to setup Bundler; you might need to `bundle install`: #{e.message}")
+end
+
 require "bundler/gem_tasks"
 require "rspec/core/rake_task"
+require "rake/clean"
+
+CLEAN.include 'build_tests_run'
 
 RSpec::Core::RakeTask.new(:spec)