selftests/ftrace: fix event-no-pid on 1-core machine

When running event-no-pid test on small machines (e.g. cloud 1-core
instance), other events might not happen:

    + cat trace
    + cnt=0
    + [ 0 -eq 0 ]
    + fail No other events were recorded
    [15] event tracing - restricts events based on pid notrace filtering [FAIL]

Schedule a simple sleep task to be sure that some other process events
get recorded.

Fixes: ebed9628f5 ("selftests/ftrace: Add test to test new set_event_notrace_pid file")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/event/event-no-pid.tc

@@ -57,6 +57,10 @@ enable_events() {
     echo 1 > tracing_on
 }
 
+other_task() {
+    sleep .001 || usleep 1 || sleep 1
+}
+
 echo 0 > options/event-fork
 
 do_reset
@@ -94,6 +98,9 @@ child=$!
 echo "child = $child"
 wait $child
 
+# Be sure some other events will happen for small systems (e.g. 1 core)
+other_task
+
 echo 0 > tracing_on
 
 cnt=`count_pid $mypid`