Refactor Node thread creation (use tokio::sync::oneshot)

[ipetr0v]

Currently two pseudo-Nodes (gRPC server and client) are using Tokio Runtime in order to run async routines:

oak/oak/server/rust/oak_runtime/src/node/grpc/server.rs

Lines 130 to 138 in 11f96d6

	let mut async_runtime = tokio::runtime::Builder::new()
	// Use simple scheduler that runs all tasks on the current-thread.
	// https://docs.rs/tokio/0.2.16/tokio/runtime/index.html#basic-scheduler
	.basic_scheduler()
	// Enables the I/O driver.
	// Necessary for using net, process, signal, and I/O types on the Tokio runtime.
	.enable_io()
	.build()
	.expect("Couldn't create an Async runtime");

oak/oak/server/rust/oak_runtime/src/node/grpc/server.rs

Line 145 in 11f96d6

let result = async_runtime.block_on(server);

And because these threads are blocked, they cannot join correctly when the Runtime is trying to stop the Node.

We might need to use tokio::sync::oneshot, that is already used by the AuxServer:

oak/oak/server/rust/oak_runtime/src/runtime/introspect.rs

Lines 170 to 176 in 38522c9

	notify_receiver: tokio::sync::oneshot::Receiver<()>,
	) {
	let mut tokio_runtime = tokio::runtime::Runtime::new().expect("Couldn't create Tokio runtime");
	tokio_runtime.block_on(futures::future::select(
	Box::pin(make_server(port, runtime)),
	notify_receiver,
	));

oak/oak/server/rust/oak_runtime/src/runtime/mod.rs

Lines 160 to 165 in 38522c9

	let (notify_sender, notify_receiver) = tokio::sync::oneshot::channel::<()>();
	info!("spawning {} server on new thread", name);
	let join_handle = thread::Builder::new()
	.name(format!("{}-server", name))
	.spawn(move || f(port, runtime, notify_receiver))
	.expect("failed to spawn introspection thread");

oak/oak/server/rust/oak_runtime/src/runtime/mod.rs

Lines 177 to 188 in 38522c9

	fn drop(&mut self) {
	let join_handle = self.join_handle.take();
	let notify_sender = self.notify_sender.take();
	if let Some(notify_sender) = notify_sender {
	info!("stopping {} server", self.name);
	notify_sender.send(()).unwrap();
	}
	if let Some(join_handle) = join_handle {
	let result = join_handle.join();
	info!("stopped {} server, result {:?}", self.name, result);
	}
	}