(QENG-1548) vcloud hypervisor improvements

This PR has two changed to the 'vcloud' hypervisor:

* 'resourcepool' is not a required parameter, as non-DRS-enabled clusters do not have resource pools
* if 'name' is a specified host parameter, a randomized hostname is not generated
I suppose it is possible for someone to set any of the host parameters to a blank value; wouldn't this be checked in a lower -level (hosts file reading/parsing) rather than in the hypervisor?