[AIRFLOW-2951] Update dag_run table end_date when state change

[YingboWang]

The existing airflow only change dag_run table end_date value when
a user teminate a dag in web UI. The end_date will not be updated
if airflow detected a dag finished and updated its state.

This commit add end_date update in DagRun's set_state function to
make up tho problem mentioned above.

Make sure you have checked all steps below.

Jira

• My PR addresses the following Airflow-2951 issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-2951
  • 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:
  Same feature was merged in master before. This PR is to backport to v1-10-test

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  tests/models.py:DagRunTest.test_dagrun_set_state_end_date

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.

Code Quality

• Passes git diff upstream/master -u -- "*.py" | flake8 --diff

@ashb @KevinYang21

[codecov-io]

Codecov Report

Merging #3990 into v1-10-test will increase coverage by <.01%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##           v1-10-test    #3990      +/-   ##
==============================================
+ Coverage       77.77%   77.78%   +<.01%     
==============================================
  Files             203      203              
  Lines           15306    15307       +1     
==============================================
+ Hits            11904    11906       +2     
+ Misses           3402     3401       -1

Impacted Files	Coverage Δ
airflow/models.py	88.76% <100%> (+0.04%)	⬆️

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[ashb]

Thanks @YingboWang

[KevinYang21]

👍 LGTM