Fix exception while catching tango exception

Closes #104 (closed)

When the device is not yet started the exception is:

PyTango.DevFailed: DevFailed[
DevError[
    desc = The polling (necessary to send events) for the attribute status is not started
  origin = DServer::event_subscription
  reason = API_AttributePollingNotStarted
severity = ERR]
DevError[
    desc = Failed to execute command_inout on device dserver/limaccds/simulator, command ZmqEventSubscriptionChange
  origin = Connection::command_inout()
  reason = API_CommandFailed
severity = ERR]
DevError[
    desc = Device server send exception while trying to register event
  origin = EventConsumer::connect_event()
  reason = API_DSFailedRegisteringEvent
severity = ERR]
]

Which can be read the following way: for error in e.args, or maybe error = e.args[0] or maybe error = e.args[-1]

Here is just a lazy fix.