[horizon] Theme customisation methods have changed, code commenting is now wrong

[odyssey4me]

In the code block https://github.com/rcbops-cookbooks/horizon/blob/master/recipes/server.rb#L388-L431 the theme_image_update_style and theme_css_update_style is described as having the options of cookbook_list or download_list, whereas the code only allows for a boolean value.

The comments come from a previous behaviour (https://github.com/rcbops-cookbooks/horizon/blob/grizzly/recipes/server.rb#L324-L384) which provided for either using remote files or cookbook files, whereas the current code only allows for the use of remote files and https://github.com/rcbops-cookbooks/horizon/blob/master/recipes/server.rb#L221-L232 has been implemented for the cookbook file that is the Rackspace logo. This probably makes sense, but the code comments should be updated to reflect the new behaviour.