Fix unknown command or namespace network vm list with esx50x

I got the following error, when I used ESXi 5.0.x.
So I changed the command for getting SSH address.

```
2014/04/07 18:06:20 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:20 [DEBUG] Background SSH connection checker is testing
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:21 opening new ssh session
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:21 starting remote command: esxcli --formatter csv network vm list
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:21 [DEBUG] Background SSH connection checker is testing
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:21 remote command exited with '1': esxcli --formatter csv network vm list
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 2014/04/07 18:06:21 Error getting SSH address: 'esxcli --formatter csv network vm list'
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: 
2014/04/07 18:06:21 /home/kusakabe/packer/packer-builder-vmware-iso: Stdout: Error: Unknown command or namespace network vm list
```