autotest: terminate FTP session after transfering files

race condition starting the second MAVProxy if the first session isn't terminated

Tools/autotest/common.py

@@ -12288,11 +12288,15 @@ switch value'''
         try:
             mavproxy.send("module load ftp\n")
             mavproxy.expect(["Loaded module ftp", "module ftp already loaded"])
+            mavproxy.send("ftp set debug 1\n")  # so we get the "Terminated session" message
             mavproxy.send("ftp get %s %s\n" % (path, tmpfile.name))
             mavproxy.expect("Getting")
             self.delay_sim_time(2)
             mavproxy.send("ftp status\n")
             mavproxy.expect("No transfer in progress")
+            # terminate the connection, or it may still be in progress the next time an FTP is attempted:
+            mavproxy.send("ftp cancel\n")
+            mavproxy.expect("Terminated session")
         except Exception as e:
             self.print_exception_caught(e)
             ex = e