Remove max height on pipelines graph

#### What does this MR do?
Removes max-height from pipeline graph

#### Why was this MR needed?
The height was originally put in place because some stages have ~20 tests, which ends up looking a little lopsided and there's a large amount of white space. The scrolling container, however, is not the best solution and ends up being more difficult to scroll around to find what you're looking for. For now we can remove the height, and eventually we'll have the similar tests collapsed.

#### Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-24_at_11.32.39_AM](/uploads/1b32403548c6f7f4189a19279f13b84b/Screen_Shot_2016-08-24_at_11.32.39_AM.png)
After:
![Screen_Shot_2016-08-24_at_11.28.57_AM](/uploads/1327e37429b881265429f559d9d56482/Screen_Shot_2016-08-24_at_11.28.57_AM.png)

See merge request !5988