Add breaking scenario and spec for #520
Fixed #520: fix incorrect html formatter behaviour when background step fails

When encountering a failure in a background step, the html formatter
incorrectly marked the previous scenario red. With this fix, the html
formatter now correctly marks the current background red and does not
touch the output of the previous scenario anymore.
Merge pull request #521 from mlex/html-formatter-incorrect-for-failing-background-step

Html formatter incorrect for failing background step