[celery] Using preferred configuration proceedure

[john-bodley]

We've been using the celery_statsd for additional Celery monitoring but have recently noticed issues with the config parsing, i.e.,

>>> from celery import Celery 
>>> 
>>> 
>>> class Config:
...     STATSD_HOST = 'localhost'
... 
>>> app = Celery(source_config=Config)
>>> app.conf.STATSD_HOST
Traceback (most recent call last):
  File ".../celery/utils/collections.py", line 130, in __getattr__
    return self[k]
  File ".../celery/utils/collections.py", line 436, in __getitem__
    return self.__missing__(key)
  File ".../celery/utils/collections.py", line 269, in __missing__
    raise KeyError(key)
KeyError: 'STATSD_HOST'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../celery/utils/collections.py", line 134, in __getattr__
    type(self).__name__, k))
AttributeError: 'Settings' object has no attribute 'STATSD_HOST'

According to the documentation it seems like the config_from_object is the suggested approach, which provides the correct behavior,

>>> app = Celery()
>>> app.config_from_object(Config)
>>> app.conf.STATSD_HOST
'localhost'
>>> 

to: @graceguo-supercat @kristw @michellethomas @mistercrunch @timifasubaa

[codecov-io]

Codecov Report

Merging #5726 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5726      +/-   ##
==========================================
+ Coverage   63.38%   63.38%   +<.01%     
==========================================
  Files         361      361              
  Lines       22995    22996       +1     
  Branches     2559     2559              
==========================================
+ Hits        14575    14576       +1     
  Misses       8405     8405              
  Partials       15       15

Impacted Files	Coverage Δ
superset/utils.py	89.15% <100%> (+0.01%)	⬆️

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