Setup continuous testing with travis, do coding style check

I really like to contribute more on ansible, however, it's kinda painful to read ansible's source code, so many [PEP8](http://legacy.python.org/dev/peps/pep-0008/) violations, unused imports, different spacing and so on, since there is basically no coding style check.

When this project comes bigger and bigger, I believe these bad coding style will soon become heavy technical debts that all ansible developers need to pay. I am not saying we should stick to all PEP8 rules, but at least, many reasonable basic rules should be ensured.

Hence, I wrote a `.travis.yml` file, for ensuring tests are ran against every single commit. It also checks the coding style.