BUG/API: info repr should honor display.max_info_columns
Closes https://github.com/pydata/pandas/issues/6939

I think this is what we agreed on. The tests are split up. In `test_format` we do more of the following global settings tests. The rest are in `test_frame` which directly call `df.info()` and I'm basically testing that the kwargs there override the global settings.
