`fence_eaton_snmp` fails with python stack trace when executed against unsupported type of EATON device.

Issue

• When fence_eaton_snmp is tested against some EATON devices it fails with following output

  Traceback (most recent call last):
    File "/usr/sbin/fence_eaton_snmp", line 235, in <module>
      main()
    File "/usr/sbin/fence_eaton_snmp", line 231, in main
      result = fence_action(FencingSnmp(options), options, set_power_status, get_power_status, get_outlets_status)
    File "/usr/share/fence/fencing.py", line 974, in fence_action
      status = get_multi_power_fn(tn, options, get_power_fn)
    File "/usr/share/fence/fencing.py", line 880, in get_multi_power_fn
      plug_status = get_power_fn(tn, options)
    File "/usr/sbin/fence_eaton_snmp", line 128, in get_power_status
      eaton_resolv_port_id(conn, options)
    File "/usr/sbin/fence_eaton_snmp", line 91, in eaton_resolv_port_id
      eaton_set_device(conn)
    File "/usr/sbin/fence_eaton_snmp", line 83, in eaton_set_device
      device = agents_dir[eaton_type[0][1]]
  KeyError: None