[AIRFLOW-3742] Fix handling of "fallback" for int/boolean config option

[ttanay]

Support for a fallback kwarg was added in AirflowConfigParser.get
in [AIRFLOW-3742], but, AirflowConfigParser.getboolean also needs
to support it.

Make sure you have checked all steps below.

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-3852
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.

Description

• Here are some details about my PR, including screenshots of any UI changes:

On the latest master, when I ran airflow worker, I got the following error:

[2019-02-09 00:12:25,983] {__init__.py:51} INFO - Using executor SequentialExecutor
Traceback (most recent call last):
File "/home/tanay/Coding/airflow/.env/bin/airflow", line 6, in <module>
exec(compile(open(__file__).read(), __file__, 'exec'))
File "/home/tanay/Coding/airflow/airflow/bin/airflow", line 32, in <module>
args.func(args)
File "/home/tanay/Coding/airflow/airflow/utils/cli.py", line 74, in wrapper
return f(*args, **kwargs)
File "/home/tanay/Coding/airflow/airflow/bin/cli.py", line 1058, in worker
if not settings.validate_session():
File "/home/tanay/Coding/airflow/airflow/settings.py", line 226, in validate_session
worker_precheck = conf.getboolean('core', 'worker_precheck', fallback=False)
TypeError: getboolean() got an unexpected keyword argument 'fallback'

Support for a fallback kwarg in AirflowConfigParser.get was added by @ashb in #4567.
Support for it also needs to be in AirflowConfigParser.getboolean.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  Not Needed.

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.
  • All the public functions and the classes in the PR contain docstrings that explain what it does

Code Quality

• Passes flake8

[codecov-io]

Codecov Report

Merging #4674 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4674      +/-   ##
==========================================
- Coverage   74.35%   74.33%   -0.02%     
==========================================
  Files         430      429       -1     
  Lines       27962    27950      -12     
==========================================
- Hits        20790    20778      -12     
  Misses       7172     7172

Impacted Files	Coverage Δ
airflow/configuration.py	92.08% <100%> (ø)	⬆️
airflow/operators/latest_only_operator.py	90% <0%> (-0.48%)	⬇️
airflow/operators/python_operator.py	95.12% <0%> (-0.15%)	⬇️
airflow/sensors/base_sensor_operator.py	97.91% <0%> (-0.05%)	⬇️
airflow/models/skipmixin.py
airflow/models/__init__.py	92.81% <0%> (+0.06%)	⬆️

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[feng-tao]

there are getint, getfloat etc in the configuration as well. Do we need to update those as well? cc @ashb

[ttanay]

Yes, we need to update getint() and getfloat() as well. Basically, any function that internally calls get().
Making the changes.

[ttanay]

Made the changes.

[ashb]

Thanks @ttanay - I have extended your PR (on your fork) slightly by adding tests :)

[ttanay]

Thanks @ashb!

[feng-tao]

lgtm