Fix iterations usage and suite name for calling tests

[lucasperin]

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.