vmm: InstaceStart returns Status Code 204 now

This request does not return a body. Also, in the swagger we
defined the expected response in case of success to be 204.

Signed-off-by: Andreea Florescu <[email protected]>

Author: andreeaflorescu

vmm/src/lib.rs

@@ -1231,7 +1231,7 @@ impl Vmm {
 
         match self.start_instance() {
             Ok(_) => sender
-                .send(Box::new(SyncOkStatus::Ok))
+                .send(Box::new(SyncOkStatus::NoContent))
                 .map_err(|_| ())
                 .expect("one-shot channel closed"),
             Err(_) => sender