[WIP] Add initial Redfish unit tests

[matejart]

This PR adds the unit tests for the Redfish systems API. This will work with python 3 only.
I added a step in the travis configuration that detects the current Python version and disables the tests if needed.

The API for Redfish is now extended to also include the new physical server properties introduced to the GUI in CloudForms 5.0.

[matejart]

@mshriver Travis is now passing in Python 3. Do you have any advice how to disable the tests that only work in Python 3 for the Python 2 version of tests?

[matejart]

The Travis checks are now passing. In the Python 3.7 configuration, it runs the new unit tests.

@miha-plesko please have a look.

[miha-plesko]

@matejart I'm overwhelmed with other projects, especially now that I've returned from a whole week of sick leave, so I'm passing the pleasure of the code review straight to the @mshriver .

On a quick scroll, however, I think you should really use pytest marker to conditionally skip tests when python version is not high enough, e.g. http://doc.pytest.org/en/latest/skipping.html#id1

@pytest.mark.skipif(sys.version_info < (3, 6), reason="requires python3.6 or higher")
def test_function():
    ...

[matejart]

Let's still review it iternally first.

I tried using @pytest.mark, but that doesn't work because pytest fails on from unittest import mock before it even gets to the (un)collection. Since unittest.mock is a Python 3 thing, and with the overall migration to Python 3.7, I was quicker and cleaner with the rm script.

[mshriver]

@matejart @miha-plesko let's make this even easier. I'm going to drop support for python <3.7 here, as I believe all teams using this library have migrated to py3 by now

Check out #412