Correct portcount in storagectl/sata section

In VirtualBox 4.3.20 the following error stops the script:
`VBoxManage: error: Unknown option: --sataportcount`

And the [VBoxManage documentation](https://www.virtualbox.org/manual/ch08.html#vboxmanage-storagectl) points that the correct syntax is portcount (instead sataportcount)
```
VBoxManage storagectl <uuid|vmname>
	--name <name>
	[--add <ide/sata/scsi/floppy>]
	[--controller <LsiLogic|LSILogicSAS|BusLogic|
	              IntelAhci|PIIX3|PIIX4|ICH6|I82078>]
	[--portcount <1-30>]
	[--hostiocache on|off]
	[--bootable on|off]
	[--remove]
```