[vsphere] find network by name and dvswitch

given a name and a switch name
or just a name and whether a dvs is desired
or just a name

When you just want the first (or only) distributed virtual switch on a given cluster, you for example call `get_raw_network(name, datacenter_name, true)` This enables a network admin to choose where a new machine will be placed on the network by moving a network to a distributed virtual switch or non distributed virtual switch.