fix(tests): replace sleep with prof_timeout in shows_history_message test for improved reliability

tests/functionaltests/test_muc.c

@@ -146,9 +146,10 @@ shows_history_message(void **state)
             "<x xmlns='jabber:x:delay' stamp='20151219T23:55:25'/>"
         "</message>"
     );
-    sleep(2);
 
+    prof_timeout(10);
     assert_true(prof_output_regex("testoccupant:.*an old message"));
+    prof_timeout_reset();
 }
 
 void