nav2_gazebo_spawner generates stderr on Focal

[AlexeyMerzlyakov]

nav2_gazebo_spawner package is generating stderr warning message during local testing on Ubuntu 20.04 with pre-Foxy installed. Fail log is as follows:

leha@leha-PC:~/navigation2_ws$ colcon test --packages-select nav2_gazebo_spawner
Starting >>> nav2_gazebo_spawner
--- stderr: nav2_gazebo_spawner                   
=============================== warnings summary ===============================
/home/leha/.local/lib/python3.8/site-packages/_pytest/junitxml.py:417
  Warning: The 'junit_family' default value will change to 'xunit2' in pytest 6.0.
  Add 'junit_family=xunit1' to your pytest.ini file to keep the current format in future versions of pytest and silence this warning.

-- Docs: https://docs.pytest.org/en/latest/warnings.html
---
Finished <<< nav2_gazebo_spawner [1.88s]

Summary: 1 package finished [2.19s]
  1 package had stderr output: nav2_gazebo_spawner

This warning was also in Bionic with ROS2 Eloquent onboard, but it was threatened as warning and appeared in stdout instead. In pytest v5.2+ the junit_family value should be explicitly specified in pytest config file: https://docs.pytest.org/en/latest/deprecations.html#junit-family-default-value-change-to-xunit2.

Supposed fix for that:

diff --git a/nav2_bringup/nav2_gazebo_spawner/setup.cfg b/nav2_bringup/nav2_gazebo_spawner/setup.cfg
index 598b7c2d..3edf46fb 100644
--- a/nav2_bringup/nav2_gazebo_spawner/setup.cfg
+++ b/nav2_bringup/nav2_gazebo_spawner/setup.cfg
@@ -2,3 +2,5 @@
 script-dir=$base/lib/nav2_gazebo_spawner
 [install]
 install-scripts=$base/lib/nav2_gazebo_spawner
+[tool:pytest]
+junit_family=xunit2

[SteveMacenski]

LGTM, please submit a PR