test_infra: Silence warnings about zombie spawned processes

--> test_infra/src/lib.rs:1307:25
     |
1307 |               let child = self
     |  _________________________^
1308 | |                 .command
1309 | |                 .stderr(Stdio::piped())
1310 | |                 .stdout(Stdio::piped())
1311 | |                 .spawn()
1312 | |                 .unwrap();
     | |_________________________^
     |
     = note: consider calling `.wait()`
     = note: not doing so might leave behind zombie processes
     = note: see https://doc.rust-lang.org/stable/std/process/struct.Child.html#warning
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#zombie_processes
     = note: `#[warn(clippy::zombie_processes)]` on by default

The API caller should ensure that they call .wait() or equivalent on the
spawned child to reap it.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

test_infra/src/lib.rs

@@ -1304,6 +1304,9 @@ impl<'a> GuestCommand<'a> {
         }
 
         if self.capture_output {
+            // The caller should call .wait() on the returned child
+            #[allow(unknown_lints)]
+            #[allow(clippy::zombie_processes)]
             let child = self
                 .command
                 .stderr(Stdio::piped())
@@ -1333,6 +1336,9 @@ impl<'a> GuestCommand<'a> {
                 ))
             }
         } else {
+            // The caller should call .wait() on the returned child
+            #[allow(unknown_lints)]
+            #[allow(clippy::zombie_processes)]
             self.command.spawn()
         }
     }