isolate_devices seems to break Terminal functionality

Hello,

I am using the latest release of the `systemdspawner` with `systemd 232`.
When trying to open a New -> Terminal, it opens briefly in a new browser tab and then closes itself. I tracked down the problem to be in the
```python
c.SystemdSpawner.isolate_devices = True
```
setting. After disabling it, everything works as expected.

Kind regards,
Nikolay