Improving Storage/Distribution related integration tests

The integration tests related to storage/distribution system are very limited. Currently, the integration tests only test a subset of the Storage system, that too as part of `content-directory` integration tests, e.g. if video creation+uploads succeeds then it means that uploads are working fine. However, we need to add comprehensive test suite for the storage subsystem, it includes:

- Add fixtures for all the lead actions .e.g.
- Creating Buckets
- Moving Buckets/Bags
- Updating Buckets
- Updating Vouchers

- Add fixtures for all worker action e.g.
- Accepting invitation
- Setting operator metadata
- Setting node operational status