make solr_request_params and fixtures reusable

[dpavam]

In their current format the params passed to all tests are very lengthy and hard to read. Ideally we could declare most of these params as fixtures once and pass them to the tests as necessary.

• Make fixtures common_params and facet_params reusable in the test suite replacing the existing parameters in @pytest.mark.parametrize
• Parameters for the test_process_faceting might not need to be parametrized and can be fixtures instead.