ThreadPoolTest rc fix (helidon-io#4460)

Signed-off-by: Daniel Kec <[email protected]>
(cherry picked from commit ab8d9e2)

common/configurable/src/test/java/io/helidon/common/configurable/ThreadPoolTest.java

@@ -561,6 +561,7 @@ public void run() {
         };
         pool.submit(task4);
         pool.shutdown();
+        assertThat(pool.awaitTermination(20, SECONDS), is(true));
         assertThat(pool.getCompletedTasks(), is(2));
         assertThat(pool.getFailedTasks(), is(2));
         assertThat(pool.getTotalTasks(), is(pool.getCompletedTasks() + pool.getFailedTasks()));