Resource pools not supported by VSphere Standard Edition

[matt-richardson]

I've found that when you clone from a template, the code expects to get the resource pool of the compute resource, and then search for a child resource pool underneath that.

However, VSphere Standard Edition does not support resource pools (well, it has a root resource pool, but doesn't support child resource pools).

I propose a change to use the root resource pool if no other resource_pool_name is supplied.

(pull request to follow shortly)