Report format reformatted towards TestHarness

• Removing internal generation of TestAsset identifiers, assuming that they are provided by the caller of the system, via the run_tests method, which now expects a 'test_asset_id' string argument, as does the 'build_test_asset' method.
• Reformatting the return values of various methods of the system, in particular, the GraphValidationTest.run_tests() method, to better align with Translator TestHarness expectations.