Fix part of py3 compatible 

This pull request fixes unsuccessful tests in `features` and `tools/test-features` on Python 3.4.
But the `issue.features` still need several hours to fix and might need to discuss in detail.

Following are the commands I ran the tests.
```
behave --tags=~@xfail features
behave --tags=~@xfail tools/test-features
behave --tags=~@xfail issue.features
```

Also `nosetests` not fully worked on py3 yet, will be the next goal.

Welcome any comment! 
@jenisys This might not be a good idea. But haven't figure out a way to support py2/3 in this kind of cases. Any idea?