coroutine: add test-aio coroutine queue chaining test case

coroutine: add test-aio coroutine queue chaining test case

Check that two coroutines can queue each other repeatedly without
hitting stack exhaustion.

Switch to qemu_init_main_loop() in main() because coroutines use
qemu_get_aio_context() - they don't know about test-aio's ctx variable.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20180322152834.12656-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>