uspace: Raise RLIMIT_RTPRIO or fail at hardening

On ARM, the iopl() call is skipped, and there's nothing else that cause harden_rt
to fail.  This went unnoticed on the Arm Chromebook where the RLIMIT_RTPRIO was 10.
On the Parallela (Linaro 14.04) the user has RLIMIT_RTPRIO of 0.

On this system, which I assume behaves the same as glibc pthreads on other systems,
every pthreads API call to set up a thread (including pthread_attr_setschedparam
and pthread_create) returned success, but the thread always exited without calling the
wrapper function in this situation.
latency-test: use awk for calculations

.. since mawk is 'Priority: required' and bc is not in the base system.