kselftests: timers: Add set-tz test case

Mika Westerberg reported a erroneous change in the error
checking of settimeofday, so I wanted to add a test to ensure
we don't trip over this again.

Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Baolin Wang <baolin.wang@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>