Use built-in rakelibdir feature

Rake by default imports all .rake files in the rakelib dir, so we can
use that rather than doing our own import loop.

rakefile

 require 'json'
 require 'rake/clean'
-require './rakefiles/helpers.rb'
-
-Dir['rakefiles/*.rake'].each do |rakefile|
-    import rakefile
-end
+require './rakelib/helpers.rb'
 
 # Build Constants
 REPO_ROOT = File.dirname(__FILE__)

rakefiles/prereqs.rake → rakelib/prereqs.rake

-require './rakefiles/helpers.rb'
-
 PREREQS_MD5_DIR = ENV["PREREQ_CACHE_DIR"] || File.join(REPO_ROOT, '.prereqs_cache')
 
 CLOBBER.include(PREREQS_MD5_DIR)