LVG module fix when using multiple devices (string to list)

I've found out that when running the pvcreate command we were passing all devices as if they were one parameter like:

```
['/sbin/vgcreate', '-s', '4', 'vg0', '/dev/xvdb /dev/xvdc']
```
while the correct way would be:
```
['/sbin/vgcreate', '-s', '4', 'vg0', '/dev/xvdb', '/dev/xvdc']
```