Only submit coveralls build for python 3.3

[aloysbaillet]

This is a proposal to submit coverage info to coveralls for a single python interpreter (I arbitrarily chose 3.3).
The average coverage value is slightly smaller this way, but at least you can track progress on coverage without receiving emails saying "coverage decreased (-2.36%)" every second commit...

That said, coverage reporting on nose2 has still issues on both travis and tox:

• Tox: when running "tox -e cov27" I get a very low coverage compared to the coveralls value (53%), and for example the nose2.plugins.loader.testclasses is reportedly only covered 35%, which is incorrect...
• Travis: even with this PR and coveralls only run on py33, I had random variations in coverage, see these 2 builds with no code change in-between: https://coveralls.io/builds/871995 and https://coveralls.io/builds/872041. And for these two builds, nose2.plugins.loader.testclasses has either 0% coverage (build 871995) or 89% (build 872041).

I'll keep looking into these...

[thedrow]

I accept aloysbaillet@f8f348f and I'd rather have both 3.3 and 2.7 on aloysbaillet@e7753bc.
coveralls is buggy so it's not a problem of submitting results only for 3.3.

[aloysbaillet]

So now tox runs both 27 and 33, and puts the result html in cover/cov27 and cover/cov33.

[bayandin]

May be should use the latest python 3.x — 3.4?

[thedrow]

@bayandin True.

[aloysbaillet]

Fair enough, and done!

[thedrow]

I still don't think that reporting coveralls for 3.3 (or a single Python version) is a good idea.
If coveralls is buggy they should be dealing with it.
Also if we do decide it's worth it:

if [[ $TRAVIS_PYTHON_VERSION == '3.3' ]]; then coveralls; fi;

is clearer.

[aloysbaillet]

A lot cleaner indeed.
I was mostly hoping to stabilise the coverage values reported by coveralls by eliminating one axis of variation. I thought that somehow coveralls was reporting one of the builds only (probably the first/last that finishes).
In my limited experiment there was still some small variation but nothing compared to the 3% jumps reported when running coveralls against multiple versions of python.
I'm happy to investigate more the issue and report any findings here and to the coveralls team.