Inset and outset border coloring is incorrect on left side border.

This patch will fix this issue.
Thanks to differences on rendering between CPU X GPU, there is a 1 pixel wide
difference in the position where the top border meets the right border (as
also the right border X bottom border).

The workaround to have a test that will work on both modes is to cover the
affected area with a white div. This patch adds inset test.
Adding tests for outset.
Cropping the ref images to save some bytes (as also adjust test borders
to match results).
auto merge of #4393 : Adenilson/servo/fixInsetOutsetColor01, r=pcwalton