Refactor disk builder for use with context manager

In preparation to further context manager related changes
in VolumeManager, LuksDevice, RaidDevice and more the
disk builder code which uses these classes needs to be
refactored beforehand to allow switching to context
manager based cascading of the storage device classes.
This commit does the refactoring and is related to
Issue #2412

kiwi/bootloader/config/base.py

@@ -93,7 +93,8 @@ def write_meta_data(
         pass
 
     def setup_disk_image_config(
-        self, boot_uuid, root_uuid, hypervisor, kernel, initrd, boot_options={}
+        self, boot_uuid=None, root_uuid=None, hypervisor=None,
+        kernel=None, initrd=None, boot_options={}
     ):
         """
         Create boot config file to boot from disk.