autotest: Add timeout to fly_mission.

Tools/autotest/arduplane.py

@@ -512,14 +512,14 @@ class AutoTestPlane(AutoTest):
 
         return self.wait_level_flight()
 
-    def fly_mission(self, filename):
+    def fly_mission(self, filename, mission_timeout=60.0):
         """Fly a mission from a file."""
         self.progress("Flying mission %s" % filename)
         self.load_mission(filename)
         self.mavproxy.send('switch 1\n')  # auto mode
         self.wait_mode('AUTO')
         self.wait_waypoint(1, 7, max_dist=60)
-        self.wait_groundspeed(0, 0.5, timeout=60)
+        self.wait_groundspeed(0, 0.5, timeout=mission_timeout)
         self.mavproxy.expect("Auto disarmed")
         self.progress("Mission OK")