Properly set width of embeddable carousels

For [#53567925] - the width was set incorrectly because the code wasn't correctly picking up which layout was being used.

https://www.pivotaltracker.com/story/show/53567925
Smarter height setting for embeddable carousels

This ought to finish the fix for [#53567925]; it's a bit smarter about setting the height of the containers, so we can hope it will fix our problem child. I'm going to deploy it to check.

https://www.pivotaltracker.com/story/show/53567925