[service-vm] Send shutdown request to exit rialto

And rialto will be in a loop of processing request till receiving
the shutdown request.

Bug: 299432766
Test: atest rialto_test
Change-Id: Ifd65adde74a370a91fc462930bb513a3e1fe65b9
diff --git a/rialto/src/communication.rs b/rialto/src/communication.rs
index ee4ecdb..50722f2 100644
--- a/rialto/src/communication.rs
+++ b/rialto/src/communication.rs
@@ -20,7 +20,7 @@
 use core::mem;
 use core::result;
 use log::info;
-use service_vm_comm::{Request, Response};
+use service_vm_comm::{Response, ServiceVmRequest};
 use tinyvec::ArrayVec;
 use virtio_drivers::{
     self,
@@ -84,7 +84,7 @@
         }
     }
 
-    pub fn read_request(&mut self) -> Result<Request> {
+    pub fn read_request(&mut self) -> Result<ServiceVmRequest> {
         Ok(ciborium::from_reader(self)?)
     }