ztest: Track skipping test versus entire suite

The addition of the assumption API introduced a bug where a skipped test
would subsequently skip later tests within the same suite. A skipped test
was being treated as an entire skipped test suite.

Keep track of tests being skipped due to skipping in the suite setup versus
being skipped within their test function.

TEST=west build -p -b native_posix tests/kernel/condvar/condvar_api/ -t run
TEST=twister -T tests/ztest -p native_posix

Signed-off-by: Aaron Massey <aaronmassey@google.com>