if the vagrant-omnibus plugin is detected and enabled for that VM, set the OMNIBUS_DOWNLOAD_DIR env var

lib/vagrant-cachier/action/configure_bucket_root.rb

@@ -15,11 +15,32 @@ module VagrantPlugins
           if !env[:cache_buckets_folder_configured] && env[:machine].config.cache.enabled?
             setup_buckets_folder
             env[:cache_buckets_folder_configured] = true
+            if cache_vagrant_omnibus?
+              setup_omnibus_cache_folder
+            end
           end
 
           @app.call env
         end
 
+        def cache_vagrant_omnibus?
+          plugin_defined = defined?(VagrantPlugins::Omnibus::Plugin)
+          puts "xxx - cap: vagrant-omnibus defined? #{plugin_defined}"
+          return false unless plugin_defined
+
+          chef_version = @env[:machine].config.omnibus.chef_version
+          puts "xxx - cap: chef_version? #{chef_version}"
+          return chef_version != nil
+        end
+
+        def setup_omnibus_cache_folder
+          # since it's not configurable via the vagrant-omnibus plugin (yet)
+          # we specify the directory where to download the omnibus package here
+          omnibus_cache_dir = File.join(cache_root.to_s, 'omnibus')
+          FileUtils.mkdir_p(omnibus_cache_dir) unless File.exist? omnibus_cache_dir
+          ENV['OMNIBUS_DOWNLOAD_DIR'] = "/tmp/vagrant-cache/omnibus"
+        end
+
         def setup_buckets_folder
           FileUtils.mkdir_p(cache_root.to_s) unless cache_root.exist?