Make TaskProcess catch all Exceptions

"except Exception" will not catch all types of exceptions.

To trigger the bug:

```python
import luigi

class BugGenerator(luigi.Task):
	p = luigi.IntParameter()

	def output(self):
		luigi.LocalTarget('/tmp/bug/{}'.format(self.p))

	def run(self):
		raise SystemExit("I'm gonna fuck you up!")


class BugSpam(luigi.Task):

	def requires(self):
		return {i: BugGenerator(p=i) for i in range(30)}

if __name__ == '__main__':
	luigi.run()
```