[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.
I realize other code in this class doesn't use parentheses around the arguments, but we're trying to standardize the code style on all new code.  Please add them in at your leisure.