Replace sleep with px4_sleep

This is another step to isolate time from the system.

src/platforms/apps.cpp.in

@@ -112,7 +112,7 @@ int wait_for_topic(int argc, char *argv[])
 
 	while (orb_exists(&meta, 0) != 0 && (timeout && (elapsed < timeout)))
 	{
-		sleep(1);
+		px4_sleep(1);
 		elapsed += 1;
 	}
 

src/platforms/px4_time.h

@@ -35,5 +35,6 @@ __END_DECLS
 #define px4_clock_settime clock_settime
 
 #define px4_usleep system_usleep
+#define px4_sleep system_sleep
 
 #endif