Make it unique by returning the pid in the start function

Signed-off-by: utam0k <[email protected]>

crates/containerd-shim-wasmedge/src/instance.rs

@@ -257,7 +257,7 @@ impl Instance for Wasi {
  cvar.notify_all();
  });
 
- Ok(0)
+ Ok(pid.as_raw() as u32)
  }
 
  fn kill(&self, signal: u32) -> Result<(), Error> {