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_test.go

@@ -1203,3 +1203,18 @@ func TestAppendFwcfg(t *testing.T) {
 	}
 	testAppend(fwcfg, fwcfgString, t)
 }
+
+func TestAppendPVPanicDevice(t *testing.T) {
+	testCases := []struct {
+		dev Device
+		out string
+	}{
+		{nil, ""},
+		{PVPanicDevice{}, "-device pvpanic"},
+		{PVPanicDevice{NoShutdown: true}, "-device pvpanic -no-shutdown"},
+	}
+
+	for _, tc := range testCases {
+		testAppend(tc.dev, tc.out, t)
+	}
+}