tools/syz-testbed: make Instance.Stop() nonblocking
tools/syz-testbed: make Instance.Stop() nonblocking

xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller