Make vagrant-vsphere work with VMWare infrastructure/clusters

The current vagrant-vsphere barfs on a cluster as a resource pool name. Calling cr.resourcePool.find returned nil and everything blew up.

This make sure to handle the case where the compute resource is a cluster by grabbing the datacenter host folder and conditionally searching based on its type.

This has been tested on a Clustered VMWare infrastructure deployment running vSphere 4.1.0