qemu: add pvpanic device to get GUEST_PANICKED event

Listening to the events channel from QEMU and a guest
panic event issued, then we can get the event and do some
work for the special event.

Fixes: #152

Signed-off-by: bin liu <bin@hyper.sh>

qemu/qemu.go

@@ -1118,6 +1118,24 @@ func (blkdev BlockDevice) deviceName(config *Config) string {
 	return string(blkdev.Driver)
 }
 
+// PVPanicDevice represents a qemu pvpanic device.
+type PVPanicDevice struct {
+	NoShutdown bool
+}
+
+// Valid always returns true for pvpanic device
+func (dev PVPanicDevice) Valid() bool {
+	return true
+}
+
+// QemuParams returns the qemu parameters built out of this serial device.
+func (dev PVPanicDevice) QemuParams(config *Config) []string {
+	if dev.NoShutdown {
+		return []string{"-device", "pvpanic", "-no-shutdown"}
+	}
+	return []string{"-device", "pvpanic"}
+}
+
 // VhostUserDevice represents a qemu vhost-user device meant to be passed
 // in to the guest
 type VhostUserDevice struct {