Modified the structure of member names to reflect the point made on t…

…he thread below.

ros-infrastructure/rep#385 (comment)

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

test/test_thread.cpp

@@ -104,7 +104,7 @@ TEST(thread, attribute) {
     rcutils_attr.core_affinity = rcutils_get_zero_initialized_thread_core_affinity();
     rcutils_attr.scheduling_policy = RCUTILS_THREAD_SCHEDULING_POLICY_FIFO;
     rcutils_attr.priority = 42;
-    rcutils_attr.name = NULL;
+    rcutils_attr.tag = NULL;
 
     attr.set_rcutils_thread_attribute(rcutils_attr);