ProcessLookupError when terminating a local ensemble

[berland]

This line:

ert/src/ert/scheduler/local_driver.py

Line 97 in 8548bcd

proc.terminate()

can trigger an error if a job has been initiated by local_driver.py but the subprocess has not yet started. Observed while bug-bashing:

Killing realization 71 failed with error 
Exception in scheduler task job-59_task: 
Traceback: Traceback (most recent call last):
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 72, in _run
    returncode = await self._wait(proc)
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 91, in _wait
    return await proc.wait()
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/subprocess.py", line 135, in wait
    return await self._transport._wait()
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/base_subprocess.py", line 235, in _wait
    return await waiter
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/private/havb/projects/ert/src/ert/scheduler/job.py", line 131, in run
    await self._submit_and_run_once(sem)
  File "/private/havb/projects/ert/src/ert/scheduler/job.py", line 119, in _submit_and_run_once
    await self.driver.kill(self.iens)
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 47, in kill
    raise err
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 40, in kill
    await self._tasks[iens]
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "/private/havb/projects/ert/src/_ert/async_utils.py", line 53, in _done_callback
    raise exc
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 76, in _run
    returncode = await self._kill(proc)
  File "/private/havb/projects/ert/src/ert/scheduler/local_driver.py", line 97, in _kill
    proc.terminate()
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/subprocess.py", line 141, in terminate
    self._transport.terminate()
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/base_subprocess.py", line 149, in terminate
    self._check_proc()
  File "/opt/rh/rh-python38/root/usr/lib64/python3.8/asyncio/base_subprocess.py", line 142, in _check_proc
    raise ProcessLookupError()
ProcessLookupError