Switch to using an rclpy context manager. (#787)

This still manages the lifetime of rclpy, but uses
less code to do so.

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

launch_pytest/test/launch_pytest/examples/check_node_msgs.py

@@ -46,14 +46,11 @@ def generate_test_description():
 
 @pytest.mark.launch(fixture=generate_test_description)
 def test_check_if_msgs_published():
-    rclpy.init()
-    try:
+    with rclpy.init():
         node = MakeTestNode('test_node')
         node.start_subscriber()
         msgs_received_flag = node.msg_event_object.wait(timeout=5.0)
         assert msgs_received_flag, 'Did not receive msgs !'
-    finally:
-        rclpy.shutdown()
 
 
 class MakeTestNode(Node):

launch_pytest/test/launch_pytest/examples/executables/talker.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import rclpy
+from rclpy.executors import ExternalShutdownException
 from rclpy.node import Node
 
 from std_msgs.msg import String
@@ -34,17 +35,12 @@ def callback(self):
 
 
 def main(args=None):
-    rclpy.init(args=args)
-
-    node = Talker()
-
     try:
-        rclpy.spin(node)
-    except KeyboardInterrupt:
+        with rclpy.init(args=args):
+            node = Talker()
+            rclpy.spin(node)
+    except (KeyboardInterrupt, ExternalShutdownException):
         pass
-    finally:
-        node.destroy_node()
-        rclpy.shutdown()
 
 
 if __name__ == '__main__':