Include sys.argv in error emails

[neilisaac]

Sometimes my team shares base tasks. When we get an error email, it's sometimes unclear which upstream task requires() the one that failed.

Following @Tarrasch's suggestion of adding command line arguments to address this.

[neilisaac]

Example email body:

A task failed when running. Most likely run() raised an exception.

Name: SubTask

Parameters:
  p: some option

Command line:
  'testtask.py' '--local-scheduler' 'TestTask' '--p' 'asdf'

Runtime error:
Traceback (most recent call last):
  File "/home/nisaac/code/luigi/luigi/worker.py", line 172, in run
    new_deps = self._run_get_new_deps()
  File "/home/nisaac/code/luigi/luigi/worker.py", line 114, in _run_get_new_deps
    task_gen = self.task.run()
  File "testtask.py", line 9, in run
    raise Exception('Intentional failure')
Exception: Intentional failure

[Tarrasch]

This makes the command look weird and hard to read I think. What about simply

command = subprocess.list2cmdline(sys.argv)

[Tarrasch]

LGTM. But the formatting looks strange to me. See my inline comment suggestion. I would rather just see:

  testtask.py --local-scheduler TestTask --p asdf

[Tarrasch]

LGTM! Will merge on green :)