Make provenance fixture use a fixed storage backend for testing
The parametrized storage fixture will be used to test all possible storage
implementations against the single fixed one in provenance.storage.
Add test for the different ProvenanceStorageInterface implementations
All possible implementations are instantiated in the storage fixture and tested
against the reference on in provenance. storage fixture. The latter is in turn
tested against the actual provenance algorithms.
Depends on D6053.