Add entries to .gitignore

Pekka is suspicious:

  OK, so why are we adding the above to to global osv.git ignore list?
  Neither of them are generated by the OS build system. If they bother
  your workflow, you can hide them in your local git configuration...

Raphael explains:

  The same applies to many files there :-) And it was already discussed
  that .gitignore could afford files that would make the OSv experience
  better.

  tracefile is always generated by the trace tool, and it just doesn't
  make sense to show it, imagine every new people to OSv needlessly
  having to add tracefile to their local git configuration.

Glauber wins:

  I agree with Raphael. We have discussed it before. This criteria of
  "generated by the build" is totally arbitrary. The real thing that
  matters is how many people are likely to have to do it locally.

  Those are quite pervasive files.

Agreed-with-Raphael-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>