nanosleep: Check relative nanosleeps as well as absolute

Add testing for relative nanosleeps

Signed-off-by: John Stultz <john.stultz@linaro.org>
Add two basic timer latency tests

Adds mqueue-lat.c which measures unresonable latencies.
This is influenced by a test by Romain Francoise, who
demonstrated a performance regression in 2.6.32.60.
See thread here:
http://www.mail-archive.com/stable@vger.kernel.org/msg29589.html

Also adds nanosleep-rel-lat, which checks for unreasonable
latencies from relative clock nanosleep calls.

Signed-off-by: John Stultz <john.stultz@linaro.org>