ztest: add test summary after all suites finish running

Add test summary after all test suites finish running.
The summary can be one-line or verbose, which is configured
with CONFIG_ZTEST_VERBOSE_SUMMARY. The one-line summary covers
overall suite stats. The verbose summary covers each test
function within the suite besides the one-line summary.

Signed-off-by: Ming Shao <ming.shao@intel.com>