Broken tests, TODOs, commented out code.

[Artem Shutak]

Igniters,

I've updated Ignite Coding Guidelines
<https://cwiki.apache.org/confluence/display/IGNITE/Coding+Guidelines>. See
'TODOs', 'Commented out code' and 'Appendices\Broken tests' sections.

The main goal is to say about current approach to broken tests: instead of
commenting out of broken test, we just mute them on TC.

-- Artem --