Error if the required storage controller not found

This commit adds a new error type that can be raised whenever a storage
controller of the required type is not found. This indicates that a user
needs to either add the storage controller manually or change their disk
configuration.

It also removes the last hardcoded instance of "SATA Controller" as a
default argument.

lib/vagrant/errors.rb

@@ -932,6 +932,10 @@ module Vagrant
       error_key(:virtualbox_disks_defined_exceed_limit)
     end
 
+    class VirtualBoxDisksControllerNotFound < VagrantError
+      error_key(:virtualbox_disks_controller_not_found)
+    end
+
     class VirtualBoxGuestPropertyNotFound < VagrantError
       error_key(:virtualbox_guest_property_not_found)
     end

plugins/providers/virtualbox/cap/cleanup_disks.rb

@@ -29,7 +29,7 @@ module VagrantPlugins
           controller = machine.provider.driver.storage_controllers.detect { |c| c.sata_controller? }
           primary_disk = controller.attachments.detect { |a| a[:port] == "0" && a[:device] == "0" }[:uuid]
 
-          unless disk_meta.nil?
+          if disk_meta
             disk_meta.each do |d|