rcutorture: Delay forward-progress testing until boot completes

Forward-progress testing can hog CPUs, which is not a great thing to do
before boot has completed.  This commit therefore makes the CPU-hotplug
operations hold off until boot has completed.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/rcutorture.c

@@ -3457,6 +3457,8 @@ static int rcu_torture_fwd_prog(void *args)
 	int tested_tries = 0;
 
 	VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
+	while (!rcu_inkernel_boot_has_ended())
+		schedule_timeout_interruptible(HZ / 10);
 	rcu_bind_current_to_nocb();
 	if (!IS_ENABLED(CONFIG_SMP) || !IS_ENABLED(CONFIG_RCU_BOOST))
 		set_user_nice(current, MAX_NICE);