Only allocate GPU if requirements need it (#102)

Now that it's possible to provide program specific resource
requirements, the GPU should be only allocated when it's requested.

There's still plenty of room for improvement here (mainly allocating
the right amount and fee GPUs), but this quick fix should help for
the most immediate issues.

crates/node/src/vmm/qemu.rs

@@ -244,7 +244,7 @@ impl Provider for Qemu {
             .args(["-qmp", &format!("tcp:localhost:{qmp_port},server")]);
 
         // TODO: When GPU argument handling is refactored, this should be fixed as well.
-        if self.config.gpu_devices.is_some() {
+        if self.config.gpu_devices.is_some() && req.gpus > 0 {
             cmd.args(parse_gpu_devices_into_qemu_params(
                 self.config.gpu_devices.as_ref().unwrap(),
             ));