Added a backward compatibility for `skipTest` method for python 2.6

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | #11
| License       | GNU GPLv3


- [x] Merge #40, #41, #42
- [x] Wait for travis response [... OK](https://travis-ci.org/alquerci/cyg-apt/builds/34092250)
- [x] Revert #40, #41, #42

closes #11