tests: Update the virtiofsd-rs cmdline

Commit ac25172176 bumps the rust
version of virtiofsd named `virtiofsd-rs`, which causes a warning
```
warning: use of deprecated parameter '--socket':
Please use the '--socket-path' option instead.
```

This commit updates the cmdline parameter accordingly.

Signed-off-by: Henry Wang <Henry.Wang@arm.com>

tests/integration.rs

@@ -141,7 +141,7 @@ mod tests {
         // Start the daemon
         let child = Command::new(virtiofsd_path.as_str())
             .args(&["--shared-dir", shared_dir])
-            .args(&["--socket", virtiofsd_socket_path.as_str()])
+            .args(&["--socket-path", virtiofsd_socket_path.as_str()])
             .args(&["--cache", cache])
             .spawn()
             .unwrap();