Move validation of throws annotation parameters to ut_executable_test #721

Currently, parameters of throws are validated when suite is built.
We should postpone the validation to runtime. That way, the anntation becomes truly dynamic as the package referenced by annotation parameter may not exist or may be invalid when suite is built (can be created dynamically).

This also seems like a better separation of responsibilities, as it is ut_executable_test that knows how to understand the text of annotation parameter rather than the ut_suite_builder.
This way suite building will not be carrying that responsibility anymore.