Remove non-blocking option.

Also, the CLI relies on xenctrl.lwt running Activations code automatically
more like the version in Mirage-xen does. It also relies on the Xs module
provided (now) by ocaml-xenstore-clients (xenstore_transport opam package)

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #3 from jonludlam/remove-blocking

Remove non-blocking option.