selftests/timers: Add missing fflush(stdout) calls

When running under a pipe, some timer tests would not report output in
real-time because stdout flushes were missing after printf()s that lacked
a newline. This adds them to restore real-time status output that humans
can enjoy.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>