Split TestExportSnapshot

TestExportSnapshot contains 3 type of tests.

• MiniCluster creating a table, taking a snapshot and running export
• Mocked snapshot running export
• tool helpers tests

since now we have everything packed in a single test. 2 and 3 ended up having a before and after that is creating a table and taking a snapshot which is not used. Move those tests out and cut some time from the test.