syscalls/getrusage04: Try guess timer granularity.

This patch adds timer granularity detection for the testcase.

The granularity of getrusage timers depends on CONFIG_HZ kernel
parameter. There is unfortunately no API to get getrusage timers
resolution but there are linux specific POSIX timers that have exactly
same granularity. These are now used to detect the expected timers
resolution.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>