tests: kernel: semaphore: better explain test failures

Debugging long-tail semaphore test failures currently is rather
annoying, both because many semaphore test failures do not print
their failing values, and because some semaphore tests do not
check return codes, leading to test failures well after the actual
failure.

Redo the semaphore tests to at least give consistent failure
messages including the actual return code and consistently check
return codes of k_sem_* APIs.

Also driveby-fix several places that used an insufficiently-
sized type to store k_uptime.

Signed-off-by: James Harris <james.harris@intel.com>