feat(vm_provision_mixin): set agent=1 on VM create for guest-agent channel

Proxmox only opens the virtio-serial channel qemu-guest-agent needs when
agent=1 is set at VM creation — without it, the agent package can be
installed but never actually reachable.

tests/test_vm_provision_mixin.py

@@ -123,6 +123,11 @@ def test_create_vm_from_cloud_init_single_nic():
     assert mock_node.qemu.post.called
     mixin._download_cloud_image.assert_called_once()
 
+    # Regression: without agent="1" Proxmox never attaches the virtio-serial
+    # channel the QEMU guest agent needs, so get_vm_status(wait_for_ip=True)
+    # can never succeed no matter what's installed inside the guest.
+    assert mock_node.qemu.post.call_args[1]["agent"] == "1"
+
     # Verify NIC config was set correctly: net0 with tag=10, DHCP enabled
     net_call_args = next(c for c in mock_vm.config.post.call_args_list if "net0" in c[1])
     assert "tag=10" in net_call_args[1]["net0"]