ftracetest: Do not use usleep directly

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/[email protected]
Reported-by: Michael Ellerman <[email protected]>
Reported-by: Dave Jones <[email protected]>
Reported-by: Luis Henriques <[email protected]>
Suggested-by: Pádraig Brady <[email protected]>
Acked-by: Steven Rostedt <[email protected]>
Acked-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>