selftests: futex: convert test to use ksft TAP13 framework

Convert test to use ksft TAP13 framework to print user friendly
test output which is consistent across kselftest suite.

Acked-by: Darren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>