Unit tests should use GcsJsonApi instead of BotoTranslation

The Class Map currently being used for [unit tests](https://github.com/GoogleCloudPlatform/gsutil/blob/0e0faf89474d591a4bd228775d4c9ac0f1ce5cbe/gslib/tests/testcase/unit_testcase.py#L75) for JSON is BotoTranslation. This is different from what we have in the [cs_api_map.GetClassMap](https://github.com/GoogleCloudPlatform/gsutil/blob/0e0faf89474d591a4bd228775d4c9ac0f1ce5cbe/gslib/cs_api_map.py#L57) method.

Instead of using a [custom method ](https://github.com/GoogleCloudPlatform/gsutil/blob/0e0faf89474d591a4bd228775d4c9ac0f1ce5cbe/gslib/tests/testcase/unit_testcase.py#L71) we should be directly using the [gslib.cs_api_map.GsutilApiClassMapFactory.GetClassMap](https://github.com/GoogleCloudPlatform/gsutil/blob/0e0faf89474d591a4bd228775d4c9ac0f1ce5cbe/gslib/cs_api_map.py#L53) in unit_testcase.py.

Doing this replacement is currently breaking a lot of unit tests which are currently relying on the BotoTranslation API even if we choose Json API. So making this change will also need fixing all the unit tests.