Beckhoff: Add test for disconnect and reconnect

[DominicOram]

As a developer I would like to be confident that the Beckhoff driver reconnects on the restart of a connection. To test this the beckhoff automation interface will have to stop the PLC from running and then start it up again. I did a naive implementation where AutomationInterface.exe stop will log in and stop the PLC then AutomationInterface.exe run will login and start it again. In this case the IOC did reconnect but PVs were still in alarm. In the case where you stop and start the PLC manually the IOC happily recovered. Therefore we should:

• Work out why the automation interface causes different behaviour in the IOC than manually restarting
• Either fix the IOC to properly reconnect or fix the automation interface to properly restart

[DominicOram]

See https://github.com/ISISComputingGroup/BeckhoffPLCCode/commit/45960fe0d60315dad6967e0ca390c17055b79672 for the naive approach