Fix SITL Test failure: Place PX4 instance runner after Gazebo server runner (#21230)

* MAVSDK_Test_Runner: Place PX4 instance runner after Gazebo server runner

- This was a nasty bug where starting PX4 instance first, then starting
  Gazebo server was causing PX4 instance' EKF to freak out, probably
because it doesn't like getting data a while after it is started
- Detailed breakdown is given here: https://github.com/PX4/PX4-Autopilot/issues/21229#issuecomment-1450761542
- This now guarantees that such edge case won't occur and MAVSDK test
  will run as it should

* MAVSDK Test Runner: Retain comment within 79 character limit

- To pass flake8 python style check

* Update test/mavsdk_tests/mavsdk_test_runner.py

Co-authored-by: Julian Oes <julian@oes.ch>

---------

Co-authored-by: Julian Oes <julian@oes.ch>

test/mavsdk_tests/mavsdk_test_runner.py

@@ -401,17 +401,6 @@ class Tester:
         self.active_runners = []
 
         if self.config['mode'] == 'sitl':
-            px4_runner = ph.Px4Runner(
-                os.getcwd(),
-                log_dir,
-                test['model'],
-                case,
-                self.get_max_speed_factor(test),
-                self.debugger,
-                self.verbose,
-                self.build_dir)
-            self.active_runners.append(px4_runner)
-
             if self.config['simulator'] == 'gazebo':
                 gzserver_runner = ph.GzserverRunner(
                     os.getcwd(),
@@ -441,6 +430,22 @@ class Tester:
                         self.verbose)
                     self.active_runners.append(gzclient_runner)
 
+                # We must start the PX4 instance at the end, as starting
+                # it in the beginning, then connecting Gazebo server freaks
+                # out the PX4 (it needs to have data coming in when started),
+                # and can lead to EKF to freak out, or the instance itself
+                # to die unexpectedly.
+                px4_runner = ph.Px4Runner(
+                    os.getcwd(),
+                    log_dir,
+                    test['model'],
+                    case,
+                    self.get_max_speed_factor(test),
+                    self.debugger,
+                    self.verbose,
+                    self.build_dir)
+                self.active_runners.append(px4_runner)
+
         mavsdk_tests_runner = ph.TestRunner(
             os.getcwd(),
             log_dir,