WIP Refactor test

[lmignon]

It's a work in progress...
The goal of this PR is to put in place CI and to refactor the tests to automatically run on a set of environments.

• Travis is used as CI. During the initialization of the build env, Alfresco 201702 is installed from docker.
• The tests were refactored to be based on pytest. Pytest allows you to run the same tests for a given list of parameters. At this point, this list includes the configuration required for browser and atompub bindings on Alfresco. (https://github.com/apache/chemistry-cmislib/compare/trunk...acsone:trunk_refactor_test?expand=1#diff-9100fb1694c64625c1d58773684b61b3R49). At the same time, explicit markers have been added to skip tests not supported by any of the Alfresco. (https://github.com/apache/chemistry-cmislib/compare/trunk...acsone:trunk_refactor_test?expand=1#diff-65845194ab3e4cd18799041f5905094dR70). The result is a test suite that ends successfully.
• Tox is used to launch the test suite. http://tox.readthedocs.io/en/latest/ Tox will allow us to run our tests at the same time on Py2 and Py3

This work is the first necessary step before adding Py3 support. Before that I will make all python files compliant with Flake8

I don't have access to the settings of this repository. Therefore I'm not able to activate travis on this repo. You can find the result of a build here https://travis-ci.org/acsone/chemistry-cmislib/builds/292630173

[lmignon]

included into #12