Change GET request to POST requests
Change GET request to POST requests

Get request should not have http body according to RFC.
Works well with POST here, and fails with GET for some cases:
2019-03-22 20:51:24,589 tornado.application[19] ERROR: Uncaught exception GET /api/add_task ...

Traceback (most recent call last):
  File "contrib/python/tornado/tornado/web.py", line 1510, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "contrib/python/luigi/luigi/server.py", line 120, in get
    result = getattr(self._scheduler, method)(**arguments)
  File "contrib/python/luigi/luigi/scheduler.py", line 819, in add_task
    assert worker is not None
AssertionError


By the way: urllib fetcher uses POST here (urlopen(full_url, body, timeout).)
adaitche/luigi,riga/luigi,adaitche/luigi,spotify/luigi,dlstadther/luigi,jamesmcm/luigi,riga/luigi,PeteW/luigi,PeteW/luigi,dlstadther/luigi,PeteW/luigi,spotify/luigi,spotify/luigi,dlstadther/luigi,PeteW/luigi,spotify/luigi,jamesmcm/luigi,riga/luigi,adaitche/luigi,jamesmcm/luigi,adaitche/luigi,riga/luigi,jamesmcm/luigi,dlstadther/luigi