[trunk] Filter scrolling for according always shows despite only having 1 item

After starting testing the "Filter" section on the machine listing page, I noticed that the scroll bar is always shown regardless of the amount of items available in the section the accordion, and honestly, it breaks visuals of the page.

[What's expect]
The expectation is that the according section only shows the scroll bar if and only if it is required. In other words, if there are too many items, the scroll bar should be present. If there's not too many, the scroll bar shouldn't be shown.

http://people.canonical.com/~andreserl/filters.png