kselftests: timers: Check _ALARM clockids are supported before suspending

It was reported that the alarmtimer-suspend test hangs on older
systems that don't support _ALARM clockids.

This is due to the fact that we don't check if the timer_create
fails, and thus when we suspend, the system will not programatically
resume.

Fix this by checking the timer_create call for errors.

Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>