fix misc. issues

`AllocateCylinder` is still broken because the `Cylinder` type cannot be used as a map key. We need to find a better way of storing `Update`s uniquely.

Also, `AllocateCylinder` must be registered with gob before being used as an rpc argument. Since `JoinRequest` requires this as well, we should move both register calls to some sort of `initialize()` function.