ftracetest: Do not use usleep directly

The usleep is only provided on distros from Redhat so running ftracetest
on other distro resulted in failures due to the missing usleep.

The reason of using [u]sleep in the test was to generate (scheduler)
events.  It can be done various ways like this:

yield() {  ping localhost -c 1 || sleep .001 || usleep 1 || sleep 1; }

For more information to the history of this patch, please refer to:

Link: http://lkml.kernel.org/r/1427329943-16896-1-git-send-email-namhyung@kernel.org



Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Reported-by: Luis Henriques <luis.henriques@canonical.com>
Suggested-by: Pádraig Brady <P@draigBrady.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>