Wait for non-child hypervisor exit before finishing kill

After a hypeman restart the hypervisor is not our child, so Wait4
returns ECHILD immediately and the kill loop finished before the
process had exited. Poll for actual process exit in that case.

Author: yummybomb

lib/instances/delete.go

@@ -220,11 +220,16 @@ func (m *manager) killHypervisor(ctx context.Context, inst *Instance) error {
 			for i := 0; i < 50; i++ { // 50 * 100ms = 5 seconds
 				var wstatus syscall.WaitStatus
 				wpid, err := syscall.Wait4(pid, &wstatus, syscall.WNOHANG, nil)
-				if err != nil || wpid == pid {
-					// Process reaped successfully or error (likely ECHILD if already reaped)
+				if err == nil && wpid == pid {
 					log.DebugContext(ctx, "hypervisor process killed and reaped", "instance_id", inst.Id, "pid", pid)
 					break
 				}
+				if err != nil {
+					if killErr := syscall.Kill(pid, 0); killErr == syscall.ESRCH {
+						log.DebugContext(ctx, "hypervisor process killed", "instance_id", inst.Id, "pid", pid)
+						break
+					}
+				}
 				if i == 49 {
 					log.WarnContext(ctx, "hypervisor process did not exit in time", "instance_id", inst.Id, "pid", pid)
 				}