Add support for fedora/27 and fedora/28 packages

What does this MR do?

Adds support for releasing packages for Fedora 27 and Fedora 28.

Why was this MR needed?

Please read #3240 (closed) and #2626 (closed) for context.

Are there points in the code the reviewer needs to double check?

Fedora 28 is not released yet, but it will be at 2018-05-01 so in less than two weeks. So I've added it now and we can benefit from it next month when Runner 10.8 will be released.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #3240 (closed)