Refactor tests for Python SDK

[kaxil]

We have tons of redundant integration tests that test the same functionality and we don't have a clear separation of unit tests and integration tests.

Acceptance Criteria:

• [ ] Devs should be able to run all the unit tests separately without having credentials for various envs that we use for integration tests
• [ ] CI should run unit-tests in a separate "single" job and run integration tests in "parallel" (like we do now)