Merge pull request #1 from justinclayton/vsphere-support

changes to support a wider range of vCenter deployments
Add additional error handling for Datacenter and Compute Resource configuration, update docs

Renamed "host" configuration to "compute_resource" to allign with vSphere documentation

Added support for retrieving the compute_resource that should support cluster configurations

Added support for validating datacenter and compute resource selection, providing sane error messages (with recovery instructions if available)
Provide error handling for datastore, network, and veewee host ip configuration

Separated out datastore and network selection logic into separate files from create.rb

Added support for validating datastore and network selection, providing sane error messages (with recovery instructions if available). Also includes validation that the compute resource can access the datastore and network desired.

Added error handling on host ip configuration to inform users of available IP addresses for the machine running veewee
Created VncError and added Vnc Error handling to build