VMware: use VM uuid for volume attach and detach

When using the instance name an exception occurs. The problem is due
to the way in which the VM's are named on vCenter. On vCenter the name
of a VM is actually the nova uuid - hence all intercations with the VM
should be done by the uuid. The problem here is that the name was used.

Fixes bug: 1208173

Change-Id: Iefe1584ee1ded403815cf0ca1fb5206ceadd3e55
Merge "VMware: use VM uuid for volume attach and detach"