Added failing test for `xunit_output` when using Background sections.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>
Updated `xunit_output` to correctly output steps executed in a background section in addition to scenarios.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>
Merge pull request #330 from subblime/master

Fixed XUnit Output for Background Sections