Fix early shutdown

If a suite has a `Jinja2TemplateError`, it can fail during the first part of `cylc run` and force a shutdown - however this currently fails with:
```
File: "/some/where/cylc/lib/cylc/scheduler.py", line 1289, in shutdown
    if self.suite.id:
AttributeError: 'start' object has no attribute 'suite_id'
```

This is because the `self.suite_id` property is not defined until `configure` in scheduler.py, and it needs a default `None` value to allow it to go through `shutdown`.

@hjoliver, please review.