feat: block netvm start until qemu responds to pings

src/host/rootfs/usr/local/bin/netvm

@@ -82,10 +82,19 @@ function cmd_start(){
                 -boot order=d \
                 -chardev socket,path=/var/run/netvm_qga.sock,server=on,wait=off,id=qga0 \
 		$net_args \
+		-device qemu-xhci \
                 -device virtio-serial \
                 -device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0 &
-        echo $! > "${LOCKFILE}"
-	#TODO: Poll here for VM to come up and respond to QMP agent ping
+        pid=$!
+	echo "$pid" > "${LOCKFILE}"
+        until qemu_ga guest-ping; do
+		ps -p $pid >/dev/null || {
+			echo "Error: netvm exited unexpectedly";
+			exit 1;
+			rm "${LOCKFILE}"
+		}
+                sleep 1
+        done
 }
 
 function cmd_stop(){