Fix iterations usage and suite name for calling tests#85

Fixes #81 and #83 Changes --- * Fix issue where the number of iterations in nested suites is not used. Example: ``` ... static MunitSuite main_suite[] = { {"unit_tests/", unit_tests, NULL, 1, MUNIT_SUITE_OPTION_NONE }, {"benchmarks/", benchmarks, NULL, 100, MUNIT_SUITE_OPTION_NONE }, { NULL, NULL, NULL, 0, MUNIT_SUITE_OPTION_NONE} }; static const MunitSuite test_suite = {"", NULL, main_suite, 1, MUNIT_SUITE_OPTION_NONE }; ``` All tests will run 1 iteration and the value 100 in `benchmark` is never accessed. * Add case to allow calling tests by their suite prefix Using the same example above, now it is possible to call the test passing `unit` or `benchmark` to execute all unit tests or benchmark tests. Previously the input arguments were required to match the test name + suite prefix. * Added a compilation flag that returns ***EXIT_FAILURE*** in case no tests are run. This is an optional feature that helps pipelines detect (by failing) in case there is a typo or some misconfiguration in the CI file calling the tests.