Enhancement/14967

I have added basic unit tests for the ganetiviz app in gwm.
['enhancement/14967'](https://code.osuosl.org/projects/ganeti-webmgr/issues/14967)

* View tests to check validity of cluster JSON output as required by ganetiviz.
* Basic Selenium unittests for the Ganetiviz UI. The test case inherits the  [LiveServerTestCase](https://docs.djangoproject.com/en/dev/topics/testing/overview/#liveservertestcase) provided by django that creates a live django server running in the background on port 8081 specially for the selenium tests.