Only take screenshot of failures if running local.

Remote tests are run on SauceLabs, which automatically handles screenshots.
You can now specify the Katello username/password.

* You can now specify the default username and password for your Katello
or SAM server. The defaults are admin/admin.
* Cleaned up code according to PEP8 warnings.
Adding decorator to skip tests.

Tests can be skipped based on the 'mode' that the server is running.