[Tables] Use AzureTestCase instead of AzureMgmtTestCase

[seankane-msft]

The test classes in testcase.py and asynctestcase.py inherit from the management plane test class.

[bradleydamato]

Hi @seankane-msft ; it looks like a change only need to be made in testcase.py as asynctestcase.py imports TableTestCase from the former.

I've run the tox tests and here are the results:

Additionally, here is a PR: #14443