Add unit tests for tempest hacking checks

This commit adds unit tests for the remaining untested hacking checks:
 - T102: import_no_clients_in_api
 - T104: scenario_tests_need_service_tags
 - T106: no_vi_headers
 - T107: service_tags_not_in_module_path

Change-Id: Ib2a82c5e92fbd7f165477f1906cf117f064fcef5
Merge "Add unit tests for tempest hacking checks"