Tools: autotest: ensure reboot if dataflash-over-mavlink test fails

Will stop cascading failures from occuring

Tools/autotest/common.py

@@ -2076,6 +2076,8 @@ class AutoTest(ABC):
 
     def test_dataflash_over_mavlink(self):
         self.context_push()
+        ex = None
+        try:
             self.set_parameter("LOG_BACKEND_TYPE", 3)
             self.reboot_sitl()
             self.wait_ready_to_arm()
@@ -2089,8 +2091,13 @@ class AutoTest(ABC):
             self.drain_mav() # hopefully draining COMMAND_ACK from that failed arm
             self.arm_vehicle()
             self.disarm_vehicle()
+        except Exception as e:
+            self.progress("Exception (%s) caught" % str(e))
+            ex = e
         self.context_pop()
         self.reboot_sitl()
+        if ex is not None:
+            raise ex
 
     def test_arm_feature(self):
         """Common feature to test."""