[AIRFLOW-6271] Printing log files read during load_test_config

[potiuk]

Airflow should show where the configuration is read from. Especially for new
user it might be confusing as it is not logged anywhere and there are several
places the configuration might be read from. 

This is printed for the main config file, but not when load_test_config is used.

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-6271

Description

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

Tests

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

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.
  • All the public functions and the classes in the PR contain docstrings that explain what it does
  • If you implement backwards incompatible changes, please leave a note in the Updating.md so we can assign it to a appropriate release

[codecov-io]

Codecov Report

Merging #6842 into master will decrease coverage by 0.28%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6842      +/-   ##
==========================================
- Coverage   84.49%   84.21%   -0.29%     
==========================================
  Files         680      680              
  Lines       38392    38395       +3     
==========================================
- Hits        32441    32335     -106     
- Misses       5951     6060     +109

Impacted Files	Coverage Δ
airflow/configuration.py	93.3% <100%> (+0.07%)	⬆️
airflow/operators/mysql_operator.py	100% <0%> (ø)	⬆️
airflow/operators/mysql_to_hive.py	100% <0%> (ø)	⬆️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	45.25% <0%> (-46.72%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
...rflow/contrib/operators/kubernetes_pod_operator.py	78.75% <0%> (-20%)	⬇️
airflow/utils/sqlalchemy.py	96.61% <0%> (ø)	⬆️
airflow/hooks/hive_hooks.py	77.6% <0%> (ø)	⬆️
... and 3 more

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[ashb]

I think these should be debug -- it's a bit too noisy and not useful to see this all the time.

[ashb]

Oh nm, this is load_test_config only :)