[tests] refactoring of saveload tests

tests/saveload/basic.i

tests/saveload/bool.c

tests/saveload/callbacks.i

tests/saveload/deps.i

tests/saveload/isset.c

tests/saveload/load_one.i

tests/saveload/multi_project.i

tests/saveload/segfault_datatypes.i

tests/saveload/sparecode.i

tests/saveload/test_config