Fix manlint issues with atf-check(1)

• Use .Bf Em/.Ef instead of prefixing lines with .Em. The forms are equivalent with traditional roff, but unnecessarily verbose. The former form applies the .Em macro to the enclosed block.
• Move EXIT_STATUS section down so the section complies with section ordering specified by mdoc(7) and enforced by manlint(1).

Bump .Dd for the change

MFC after: 1 week
Sponsored by: Dell EMC Isilon