tests: added travis.yml to run unit test of pull requests on travis-ci.org

I would like to do another try to integrate the free for open source projects unit test service travis-ci.org into ansible.

## Why?
- It makes people more sensible implementing unit test, if they see, each and every pull request will be tested against regression errors.
- does not cost a dime.
- transparency.
- easy and simple, like ansible.

## How?
1. sign in on travis-ci.org using your github account (oauth)
2. go to https://travis-ci.org/profile.
3. activate the ansible/ansible repo.
4. merge this PR.

## Preview how it would look:
https://github.com/resmo/ansible/pull/1