[Batch] Migrate to new test class inheritance and structure

[mccoyp]

Description

This PR updates test_batch.py to have its test class inherit from AzureMgmtRecordedTestCase instead of AzureMgmtTestCase. The former class is necessary for test proxy use, which Batch will eventually migrate to as part of track 2 migration. Tests functionally work the same as before, but now use pytest-style assertions instead of unittest.TestCase ones.

AzureMgmtTestCase, and other test tooling that predates the test proxy, will soon be removed from the Python repository. Since vcrpy scrubbers are also no longer used in SDK tests, portions of test tooling that reference scrubbers have either been removed or updated to reference test proxy sanitizers.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[wiboris]

looks good