Code review comment for lp:~smoser/curtin/trunk.lp1523779

The change as it is right now is to add a method 'extract_storage_ordered_dict' to get an ordered dictionary, where that code was being done inside 'meta_custom' directly.

The reason for doing that is that we need to use it from curthooks.
Previously, if custom storage was used and 'grub_device' existed on a partition it woudl fail.
That was because we could only look up by serial or path.

Now, we use extract_storage_ordered_dict method to get an ordered dictionary and then get a path to that volume (or partition) via get_path_to_storage_volume.

I dont like the inline import : i've done that here only because I dont like importing from block_meta at all. I'd rather move all this to curtin.block but I dont think its ready to go there yet.

I could add another method in block_meta that
  get_path_to_storage_voulme_with_config_id() or seomthing like that and then only use one method from curthooks.