Add private network configuration to customization_spec for vSphere.
clone: make it possible to clone from a VM instead of a template

This is useful when you don't have DRS enabled, and thus are prevented
from using templates as the cloning source.

I've implemented this to have as little impact as possible on the
existing implementation by using a new configuration option
"clone_from_vm". If this option is true, vagrant-vsphere (perphaps
somewhat unintuitively?) reuses the template_name as the name of the
VM to clone from and disables any error for resource pool and compute
resource. In short, the only thing we need to do in order to clone from
a VM is to not specify a pool for the VirtualMachineRelocateSpec.
docs: add documentation for vm-cloning
merge niyue and handle multiple networks
Merge branch 'clone-vm' of https://github.com/catharsis/vagrant-vsphere into catharsis-clone-vm
simplify location spec creation, update version and readme'
add note about for cloning from VMs and for setting IP addresses
update readme