Increase the timeout in wait_for_topic_launch_test. (ros2#377)

In commit 0c081a7
(ros2#360) we increased
the timeout to 10 seconds to accomodate slower discovery.
However, this was partially reverted in
2d125a5
(ros2#353).

Restore the 10 second timeout to avoid flakes on the
buildfarm.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

Author: clalancette

launch_testing_ros/test/examples/wait_for_topic_launch_test.py

@@ -64,7 +64,7 @@ def test_topics_successful(self, count):
 
             # Method 1 : Using the magic methods and 'with' keyword
             with WaitForTopics(
-                topic_list, timeout=2.0, messages_received_buffer_length=10
+                topic_list, timeout=10.0, messages_received_buffer_length=10
             ) as wait_for_node_object_1:
                 assert wait_for_node_object_1.topics_received() == expected_topics
                 assert wait_for_node_object_1.topics_not_received() == set()