[AIRFLOW-4750] Log identified zombie task instances

[chrismclennon]

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"
  • AIRFLOW-4750

Description

While troubleshooting task instances that were unexpectedly killed I found it helpful to confirm whether the task was identified as a zombie by printing to log.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  • No unit test appears to be productive for printing to log.

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

Code Quality

• Passes flake8

[codecov-io]

Codecov Report

Merging #5389 into master will increase coverage by 0.18%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5389      +/-   ##
==========================================
+ Coverage   78.75%   78.94%   +0.18%     
==========================================
  Files         481      481              
  Lines       30201    30203       +2     
==========================================
+ Hits        23786    23843      +57     
+ Misses       6415     6360      -55

Impacted Files	Coverage Δ
airflow/utils/dag_processing.py	60.27% <100%> (+0.13%)	⬆️
airflow/operators/postgres_operator.py	0% <0%> (-100%)	⬇️
airflow/hooks/postgres_hook.py	94.64% <0%> (-1.79%)	⬇️
airflow/hooks/dbapi_hook.py	86.84% <0%> (-0.88%)	⬇️
airflow/models/connection.py	65% <0%> (+1.11%)	⬆️
airflow/hooks/hive_hooks.py	77.72% <0%> (+1.77%)	⬆️
airflow/utils/sqlalchemy.py	79.76% <0%> (+3.57%)	⬆️
airflow/operators/mysql_operator.py	100% <0%> (+100%)	⬆️
airflow/operators/mysql_to_hive.py	100% <0%> (+100%)	⬆️

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[tooptoop4]

Log does not have the word zombie?

[ashb]

As pointed out by tooptoop4 (and lets make the dates logged by iso8601 format rather than "almost")

[chrismclennon]

Good recommendations. I've adjusted the language a bit and added isoformat. Thanks