TST: Start using py.test

[max-sixty]

from #13091

Currently most of the tests pass with pytest, but there are 69 that don't. Most of these look like they're pickle or SQL / external resources issues.

pytest output here: https://gist.github.com/MaximilianR/225a071337e335ebdcc1d17637126126

So this does need a champion who could work through those issues. That's probably not me at the moment, but you have my moral support!

mpl is converting!
matplotlib/matplotlib#5405

[jreback]

those fails are because we abusing nose a bit to be more parameterized (by using yield).

[kawochen]

Did you mean generative tests? pytest has a similar thing.

[jreback]

yes, but actually wouldn't do that. These really should be parameterized test in py.test. This was a hack in nose to get it to work.

[par2]

I'd like to switch to pytests eventually, but 8/9 of my errors are related to pandas._testing.assert_almost_equal. Can this be fixed too?

[jreback]

@par2 need someone to work thru all of these issues.