Replace ATF+Kyua with something lighter

The ATF suite is really heavyweight, and we are not really using it's full potential. Something simpler like C-TAP Harness could be used instead.

Requirements:

• Support for all our supported platforms (Linux, BSDs)
• Support for all our best-effort platforms (Windows, Solaris) (?)
• Support for mocking objects
• Support for catching assertions
• Output in Test Anything Protocol
• Output in xUnit/jUnit
• Active upstream development