ztest: allow asserts anywhere

Updates the ztest_test_fail() function to allow failures in setup.
When executed, a failed assert will fail every test in the suite owning
the setup function. This was verified by adding a suite which asserts
in the setup function and has a test that should pass. During
exeuction, ztest marks the test as failing.

In order to verify exection I also added 2 new APIs:
- ZTEST_EXPECT_FAIL(suite_name, test_name)
- ZTEST_EXPECT_SKIP(suite_name, test_name)

Signed-off-by: Yuval Peress <peress@google.com>