Revert the `.travis.yml` changes.

* We still support python 2.6
* DO NOT use system packages as the travis docs clearly state.
Install patched M2Crypto.
Always define `arg` before the new line detection regarding yaml's `safe_load`.
Fix expected comment in testcase `states.pip.PipStateTest.test_pip_installed_weird_install`.
Merge pull request #4052 from s0undt3ch/hotfix/fix-travis-again

Fix travis and tests