vmware: Fixes VMDK volume incompatibility issue

VMDK volume created in a cluster having ESXi 5.1 host has a high
hardware version i.e. 9; hence, fails when attached to instance
on an ESXi 5.0 host. This patch sets the hardware version to 8,
so that the volume can be attached to instances on any ESXi host
starting version 5.0 and above.

Change-Id: Ia750fd1183334005a834eb49be767451d87b338c
Closes-Bug: #1325586
Merge "vmware: Fixes VMDK volume incompatibility issue"